CAIRO — Egyptian opposition groups gathered on Monday for a seventh day in the central Liberation Square, seeking to maintain the momentum of their uprising against President Hosni Mubarak as the army struggled to control a capital seized variously by fears of chaos and euphoria that change may be imminent. Organizers said they were calling for the largest demonstrations yet, a “march of millions,” on Tuesday.

As an early mist hung over the square, some protesters who had stayed there all night in defiance of a curfew began chanting “Down, down Mubarak,” news reports said. Army troops checked the identity of people entering the square and threw a cordon of razor wire around its access routes, news reports said, but there were no immediate reports of clashes with protesters who have cast the military as their ally and protector.

Israel, meanwhile, was reported to have called on the United States and a number of European countries over the weekend to mute criticism of Mr. Mubarak to preserve stability in the region, according to the Israeli newspaper Haaretz.

But an Israeli government official, speaking on condition of anonymity because of the delicacy of the issue, said that the Haaretz report does not reflect the position of the prime minister, Benjamin Netanyahu. Mr. Netanyahu spoke cautiously in his first public remarks on the situation in Egypt, telling his cabinet that the Israeli government’s efforts were “designed to continue and maintain stability and security in our region.”

“I remind you that the peace between Israel and Egypt has endured for over three decades and our goal is to ensure that these relations continue,” he said on Sunday as Egypt’s powerful Muslim Brotherhood and the secular opposition banded together around a prominent government critic to negotiate for forces seeking the fall of Mr. Mubarak.

The announcement that the critic, Mohamed ElBaradei, would represent a loosely unified opposition reconfigured the struggle between Mr. Mubarak’s government and a six–day–old uprising bent on driving him and his party from power.

Though lacking deep support on his own, Dr. ElBaradei, a Nobel laureate and diplomat, could serve as a consensus figure for a movement that has struggled to articulate a program for a potential transition. It suggested, too, that the opposition was aware of the uprising’s image abroad, putting forth a candidate who might be more acceptable to the West than beloved in Egypt.

In scenes as tumultuous as any since the uprising began, Dr. ElBaradei defied a government curfew and joined thousands of protesters on Sunday evening in Liberation Square, a downtown landmark that has become the epicenter of the uprising and a platform, writ small, for the frustrations, ambitions and resurgent pride of a generation claiming the country’s mantle.

“Today we are proud of Egyptians,” Dr. ElBaradei told throngs who surged toward him in a square festooned with banners calling for Mr. Mubarak’s fall. “We have restored our rights, restored our freedom, and what we have begun cannot be reversed.”

Dr. ElBaradei declared it a “new era,” and as night fell there were few in Egypt who seemed to disagree.

Dr. ElBaradei also criticized the Obama administration, as Secretary of State Hillary Rodham Clinton delivered the message via Sunday news programs in Washington that Mr. Mubarak should create an “orderly transition” to a more politically open Egypt, while she refrained from calling on him to resign. That approach, Dr. ElBaradei said, was “a failed policy” eroding American credibility.

“It’s better for President Obama not to appear that he is the last one to say to President Mubarak, it’s time for you to go,” Dr. ElBaradei said.

The tumult Sunday seemed perched between two deepening narratives: a vision of anarchy offered by the government, and echoed by Egyptians fearing chaos, against the perspective of protesters and many others that the uprising had become what they called “a popular revolution.”

The military, Egypt’s most powerful institution and one embedded deeply in all aspects of life here, reinforced parts of the capital Sunday. It gathered as many as 100 tanks and armored carriers at the Tomb of the Unknown Soldier, the site of President Anwar el–Sadat’s assassination in 1981, which brought Mr. Mubarak to power. The Interior Ministry announced it would again deploy once–ubiquitous police forces — despised by many as the symbol of the daily humiliations of Mr. Mubarak’s government — across the country, except in Liberation Square.

In a collapse of authority, the police withdrew from major cities on Saturday, giving free rein to gangs that stole and burned cars, looted shops and ransacked a fashionable mall, where dismembered mannequins for conservative Islamic dress were strewn over broken glass and puddles of water. Thousands of inmates poured out of four prisons, including the country’s most notorious, Abu Zaabal and Wadi Natroun. Checkpoints run by the military and neighborhood groups, sometimes spaced just a block apart, proliferated across Cairo and other cities.

Many have darkly suggested that the government was behind the collapse of authority as a way to justify a crackdown or discredit protesters’ calls for change.

“Egypt challenges anarchy,” a government–owned newspaper declared Sunday.

“A Conspiracy by Security to Support the Scenario of Chaos,” replied an independent newspaper in a headline that shared space at a downtown kiosk.

The United States said it was organizing flights to evacuate its citizens on Monday, and the American Embassy urged all Americans to “consider leaving as soon as they can safely do so,” in a statement that underlined a deep sense of pessimism among Egypt’s allies over Mr. Mubarak’s fate.

Turkey, a major power in the region, said it was sending three flights to evacuate 750 of its citizens from Cairo and Alexandria.

“We’re worried about the chaos, sure,” said Selma al–Tarzi, 33, a film director who had joined friends in Liberation Square. “But everyone is aware the chaos is generated by the government. The revolution is not generating the chaos.”

Still, driven by instances of looting — and rumors fed by Egyptian television’s unrelenting coverage of lawlessness — it was clear that many feared the menace could worsen, and possibly undermine the protesters’ demands.

“At first the words were right,” said Abu Sayyid al–Sayyid, a driver. “The protests were peaceful — freedom, jobs and all that. But then the looting came and the thugs and thieves with it. Someone has to step in before there’s nothing left to step into.”

For a government that long celebrated the mantra of Arab strongmen — security and stability — Mr. Mubarak and his officials seemed to stumble in formulating a response to the most serious challenge to his rule. Mr. Mubarak appeared on state television on Sunday in a meeting with military chiefs in what was portrayed as business as usual. Through the day, the station broadcast pledges of fealty from caller after caller.

“Behind you are 80 million people, saying yes to Mubarak!” one declared.

That was the rarest of comments across Cairo, though, as anger grew at what residents described as treason and betrayal on the part of a reeling state.

For two days, clashes raged at Abu Zaabal, the prison north of Cairo, and officials said the police had killed at least 12 inmates there before abandoning it. On Sunday, scores of people passed in and out of the colonnaded entrance, hauling boxes and furniture through a black iron gate. Two army tanks parked nearby declined to intervene.

The Muslim Brotherhood said 34 of its members walked out of Wadi Natroun, on the road to Alexandria, after guards abandoned their posts. All had been arrested before dawn Friday, the biggest day of the protests.

“The prisoners themselves freed us from the gang who kidnapped us, this government that has become a gang,” said Essam al–Arian, one of the Brotherhood’s leaders, who had been among those held.

Since the uprising began last week, the Brotherhood has taken part in the protests but shied away from a leadership role, though that appeared to change Sunday. Mohammed el–Beltagui, a key Brotherhood leader and former Parliament member, said an alliance of the protest’s more youthful leaders and older opposition figures had met again in an attempt to assemble a more unified front with a joint committee.

It included Dr. ElBaradei, along with other prominent figures like Ayman Nour and Osama al–Ghazali Harb, who have struggled to build a popular following. By far, the Brotherhood represents the most powerful force, but Mr. Beltagui and another Brotherhood official, Mohamed el–Katatni, said the group understood the implications of seeking leadership in a country still deeply divided over its religious program.

“We’re supporting ElBaradei to lead the path to change,” Mr. Beltagui said as he joined him in Liberation Square. “The Brotherhood realizes the sensitivities, especially in the West, towards the Islamists, and we’re not keen to be at the forefront.”

“We’re trying to build a democratic arena before we start playing in it,” he said.

Whether Dr. ElBaradei can emerge as that consensus figure remained unclear. He won the Nobel Peace Prize in 2005 for his work leading the United Nations nuclear watchdog, the International Atomic Energy Agency.

Even in Liberation Square, the crowd’s reaction to Dr. ElBaradei was mixed — some were sympathetic but many more were reserved in their support for a man who has spent much time abroad.

One Brotherhood supporter, Mohammed Fayed, an engineer, said that even if Dr. ElBaradei could replace Mr. Mubarak, he should stay no longer than a year: “ElBaradei doesn’t live here and doesn’t know us. We need a leader who can understand Egyptians.”

Whatever his success, the army, long an institution shielded from criticism in the state media, was still the fulcrum of events, with a growing recognition that it would probably play the pivotal role in shaping the outcome.

In a show of authority, Mr. Mubarak was shown meeting with Defense Minister Mohammed Tantawi and Omar Suleiman, his right–hand man and the country’s intelligence chief, whom he appointed as vice president on Saturday. In slogans and actions, protesters cultivated the military, too, in a bid to turn it to their side.

Military helicopters circled Liberation Square through the day, and jets roared across a late afternoon sky. But the army took no steps against the protesters, who cheered as the helicopters passed overhead. In an unprecedented scene, some of them lofted a captain in uniform on their shoulders, marching him through a square suffused with demonstrators that cut across Egypt’s entrenched lines of class and religious devotion.

In contrast to the apprehension elsewhere in Cairo, a carnival atmosphere descended on the square, where vendors offered Egyptian dishes at discount prices and protesters posed for pictures beside tanks scrawled with slogans like, “30 years of humiliation and poverty.”

“The people and the army are one hand!” they shouted.

Across the capital, youths and some older men guarded their own neighborhoods, sometimes posting themselves at each block and alley. Several said they were in contact with the military, as well as with each other, and many residents expressed pride in the success that they had in securing their property from the threat of looters and thieves.

The sentiments captured what has become a powerful theme these days in Cairo: that Egyptians again were taking control of their destiny, against the odds.

“We know each other, we stand by each other and people respect what we’re doing,” said Ramadan Farghal, who headed one self–defense group in the poorer neighborhood of Bassateen. “This is the Egyptian people. We used to be one hand.”

Kareem Fahim, Liam Stack, Mona El–Naggar and Dawlat Magdy contributed reporting from Cairo, and Isabel Kershner from Jerusalem.

Protest’s Old Guard Falls In Behind the Young

Cairo — Last Thursday, a small group of Internet–savvy young political organizers gathered in the Cairo home of an associate of Mohamed ElBaradei, the diplomat and Nobel laureate.

They had come to plot a day of street protests calling for the ouster of President Hosni Mubarak, but within days, their informal clique would become the effective leaders of a decades–old opposition movement previously dominated by figures more than twice their age.

“Most of us are under 30,” said Amr Ezz, a 27–year–old lawyer who was one of the group as part of the April 6 Youth Movement, which organized an earlier day of protests last week via Facebook. They were surprised and delighted to see that more than 90,000 people signed up online to participate, emboldening others to turn out and bringing tens of thousands of mostly young people into the streets.

Surprised by the turnout, older opposition leaders from across the spectrum — including the outlawed Muslim Brotherhood; the liberal protest group the Egyptian Movement for Change, known by its slogan, “Enough”; and the umbrella group organized by Dr. ElBaradei — joined in, vowing to turn out their supporters for another day of protest on Friday. But the same handful of young online organizers were still calling the shots.

They decided to follow a blueprint similar to their previous protest, urging demonstrators to converge on the central Liberation Square. So they drew up a list of selected mosques around Cairo where they asked people to gather at Friday Prayer before marching together toward the square. Then they distributed the list through e–mail and text messages, which spread virally. They even told Dr. ElBaradei which mosque he should attend, people involved said.

“What we were hoping for is to have the same turnout as the 25th, so we wouldn’t lose the numbers we had already managed to mobilize,” Mr. Ezz said.

Instead, more than 100,000 people poured into the streets of the capital, pushing back for hours against battalions of riot police, until the police all but abandoned the city. The demonstrations were echoed across the country.

The huge uprising has stirred speculation about whether Egypt’s previously fractious opposition could unite to capitalize on the new momentum, and about just who would lead the nascent political movement.

The major parties and players in the Egyptian opposition met throughout the day Sunday to address those questions. They ultimately selected a committee led by Dr. ElBaradei to negotiate directly with the Egyptian military. And they settled on a strategy that some in the movement are calling “hug a soldier” to try to win the army’s rank and file over to their side. But both newcomers and veterans of the opposition movement say it is the young Internet pioneers who remain at the vanguard behind the scenes.

“The young people are still leading this,” said Ibrahim Issa, a prominent opposition intellectual who attended some of the meetings. And the older figures, most notably Dr. ElBaradei, have so far readily accepted the younger generation’s lead, people involved said. “He has been very responsive,” Mr. Issa said. “He is very keen on being the symbol, and not being a leader.”

After signs that President Mubarak’s government might be toppling, leaders of Egypt’s opposition — old and new — met Sunday to prepare for the next steps. The first meeting was a gathering of the so–called shadow parliament, formed by older critics of the government after blatantly rigged parliamentary elections last fall. Those elections eliminated almost every one of the small minority of seats held by critics of Mr. Mubarak, including 88 occupied by Muslim Brotherhood members.

Among those present were many representatives of the Brotherhood, the former presidential candidate Ayman Nour and representatives of Dr. ElBaradei’s umbrella group, the National Association for Change, which has been working for nearly a year to unite the opposition around demands for free elections. At the end of the meeting, they had settled on a consensus list of 10 people they would delegate to manage a potential unity government if Mr. Mubarak resigned. And though the religiously conservative Brotherhood was the biggest force in the shadow parliament, the group nonetheless put Dr. ElBaradei at the top of its list. Officials of the Brotherhood said he would present an unthreatening face to the West.

A second meeting, at the headquarters of the Wafd Party, brought together four of the tiny but legally recognized opposition parties. Critics of Egypt’s authoritarian government often accuse the recognized parties of collaborating with Mr. Mubarak in sham elections that create a facade of democracy. In this case, people involved in the deliberations said, the parties could not agree on how hard to break with the president. One party, the Democratic Front, insisted they demand that Mr. Mubarak resign immediately, like protesters were doing in the streets. The other three wanted a less confrontational statement, people briefed on the outcome said.

The third meeting took place late in the afternoon outdoors, in Liberation Square, the center of the protests for the last several days, said Mr. Issa, who participated. It was brought together mainly by the younger members, organized as the April 6 Youth Movement, after the date a textile workers’ strike was crushed three years ago, and We Are All Khalid Said, after the name of a man whose death in a brutal police beating was captured in a photograph circulated over the Internet. But the meeting also brought together about 25 older figures, including opposition intellectuals like Mr. Issa. Also present were representatives of Dr. ElBaradei’s National Association for Change, which includes officials of the Muslim Brotherhood.

Mr. Issa and people briefed on that meeting said the older figures offered to help the young organizers who had started it all. Those organizers, Mr. Ezz and Mr. Issa said, knew that that the uprising had now acquired a life of its own beyond their direction, spread and coordinated by television coverage instead of the Internet. And they knew that the movement needed more seasoned leaders if Mr. Mubarak resigned, Mr. Ezz said. “Leadership has to come out of the people who are already out there, because most of us are under 30,” he said. “But now they recognize that we’re in the street, and they are taking us seriously.”

The group’s goal now, Mr. Ezz said, was to guide the protesters’ demands, chief among them the resignation of Mr. Mubarak, formation of an interim government, and amendments to the Constitution to allow for free elections. The group settled more firmly on Dr. ElBaradei, consulting with a group of other opposition figures, to speak for the movement, Mr. Issa said. Specifically, he said, the group expected Dr. ElBaradei to represent the protesters to the United States, a crucial Egyptian ally and benefactor, and in negotiations with the army, which the group expected to play the pivotal role in the coming days and weeks.

Mr. Ezz said the group also discussed future tactics, including strikes, civil disobedience and a vigil for dead protesters, as well as music performances and speakers in Liberation Square.

Others briefed on the meeting said that the group had also decided to encourage protesters to adopt the “hug a soldier” strategy. With signs that the military appeared divided between support for the president and the protesters, these people said, the group decided to encourage demonstrators to emphasize their faith and trust in the soldiers.

“We are dealing with the army in a peaceful manner until it proves otherwise, and we still have faith in the army,” Mr. Ezz said. “Until now, they are neutral, and at least if we can’t bring them to our side, we don’t want to lose them.”

Then, Mr. Issa said, it was the young organizers who directed Dr. ElBaradei to appear Sunday afternoon, after the curfew, in Liberation Square, to speak for the first time as the face of their movement.