CAIRO — A new rally by nearly 100,000 protesters in central Cairo and behind-the-scenes diplomacy from the Obama administration piled more pressure on President Hosni Mubarak today to make a swift exit from office and allow a temporary government to embark on an immediate path toward democracy.

Two days of wild clashes in central Cairo between protesters and regime supporters that killed 11 people this week seemed to have pushed the United States to the conclusion that an Egypt with Mubarak at the helm is potentially more unstable than one without him.

For the first time in the 11-day-old wave of protests, varying scenarios were being put forward by two opposing camps in Egypt and by the United States over how to usher the country into a post-Mubarak era after nearly 30 years of his authoritarian rule.

President Barack Obama’s administration has made a judgment that Mubarak has to go soon if the crisis is to end peacefully, and it is in talks with Egyptian officials over the transition, according to U.S. officials.

Under one U.S. proposal, the 82-year-old Mubarak would step down and hand power to a military-backed temporary government headed by his newly appointed Vice President Omar Suleiman, the officials said, speaking on condition of anonymity to discuss the sensitive talks. The government would prepare for free and fair elections later this year.

That would mesh in some ways with the demands of the protesters. But one significant difference was the timetable.

Nobel Peace laureate Mohamed ElBaradei, one of the leaders of the protesters, criticized the government’s plan to reform the constitution within five months so presidential elections can be held on schedule in September. He said that was too rushed and indicated the regime was not serious about real change.

It would take a full year under a transitional government, he said, to sufficiently loosen the ruling party’s entrenched monopoly on Egypt’s politics before a truly election to be held. The ruling party has squeezed out almost all rivals with a grip solidified in vote fraud, election rules tilted in its favor, widespread patronage, emergency laws and domination of media.

“People are not stupid … This is not really a genuine desire to go for reform,” ElBaradei said of the government’s September timeframe. He said Mubarak must “hear the clear voice coming from the people and leave in dignity.”

But Mubarak has staunchly refused to step down, and his prime minister said today that stance is “unlikely” to change.

Mubarak insists he must serve out the rest of his term until September to ensure stability. He warned in an interview with ABC News that chaos would ensue if he leaves.

“You don’t understand the Egyptian culture and what would happen if I step down now,” he said he told Obama.

Protesters vow to keep going until he does, and today they seemed flush with a sense of victory and recharged determination after repelling pro-regime rioters who attacked the square on Wednesday, sparking 48 hours of mayhem and pitched battles. Nearly 100,000 people packed downtown Cairo’s Tahrir, or Liberation, Square today in the biggest protest in days demanding Mubarak go now.

Thousands including families with children flowed over bridges across the Nile into Tahrir, a sign that the movement was not intimidated after fending off everything thrown at them by Mubarak supporters – storms of hurled concrete, metal rebar and firebombs, charges by whip-wielding fighters on horses and camels and automatic gunfire barrages.

The ruling National Democratic Party, accused by protesters of organizing the attack, called on supporters today to “adhere to a truce and not enter confrontations with others,” but it denied any role in the assault. Protesters says the regime organized the force using police in civilian clothes and paid thugs.

Suleiman and Prime Minister Ahmed Shafiq promised no action would be taken against the protest camp. A curfew in place for a week was eased Friday, now running from 7 p.m. to 6 a.m. instead of 5 p.m. to 7 a.m.

Protesters in the square held up signs reading “Now!” and labeled the rally “the Friday of departure,” in hopes it would be the day Mubarak goes. At one point, the crowd seemed to be a field of waving Egyptian red-black-and-white flags.

Thousands prostrated themselves in the noon Muslim prayers then – immediately after uttering the prayer’s concluding “God’s peace and blessings be upon you” – they launched into chants of “Leave! Leave! Leave!” A man was lifted in his wheelchair over the heads of the crowd and he pumped his arms in the air.

Soldiers at the square’s entrances checked IDs to ensure those passing inside were not police in civilian clothes or ruling party members and performed body searches, a sign that Egypt’s most powerful institution was sanctioning the demonstration. The protesters themselves set up another ring of checks inside the army cordon.

In the morning, Egyptian Defense Minister Hussein Tantawi visited the square, the highest government figure to do so. He reviewed troops stationed there and mingled with protesters, trying to convince them that most of their demands have been met and they should go home.

The pro-government rioters of the past two days largely disappeared. In the afternoon, small groups of Mubarak supporters tried to move on the square from two directions, banging with sticks on metal fences to raise an intimidating clamor. But protesters throwing rocks pushed them back. More than two dozen people were injured, most of them lightly.

The Arabic news network Al-Jazeera said a “gang of thugs” stormed its offices in a continuation of attacks on journalists by regime supporters that erupted Thursday. It said the attackers burned the office and damaged equipment. The editor of the Muslim Brotherhood’s website, Abdel-Galil el-Sharnoubi, told the AP that policemen stormed its office Friday morning and arrested 10 to 15 of its journalists. Also clashes with sticks and fists between pro- and anti-government demonstrators erupted in two towns in southern Egypt.

On the other side of Cairo, dozens of regime supporters carrying machetes and sticks set up an impromptu checkpoint on the ring-road highway encircling the city of 18 million. They stopped cars, asking for IDs, apparently trying to root out people heading to Tahrir to join the protest. One of the armed men wore a sign reading, “We are sorry, Mr. President.”

Arab League chief Amr Moussa appeared in the square today to visit the protesters in what appeared to be a trial balloon for running for Egypt’s presidency.

His convoy was greeted by supporters with chants of “we want you as president, we want you as president.” Moussa, previously a foreign minister under Mubarak, has an elder statesman appeal for some Egyptians, boosted by his tough rhetoric against Israel.

Asked earlier by France’s Europe 1 radio if he would consider a role in the transitional government or an eventual presidential run, Moussa replied, “Why say no?”

The atmosphere in the square was relaxed. Many brought fresh bread, water, fruit and other supplies. Long lines formed at tables of people handing out tea and bread. Several celebrities of Egyptian cinema and TV joined the march, including Sherihan, a beloved screen beauty from the 1980s and early 1990s who largely disappeared from the public eye because of health issues.

Many of the protesters involved in the fighting still wore tattered bandages. Around the square were makeshift clinics, set up in the entrances of stores, including a KFC. Above one was the sign of an interlocking crescent and cross, the signs of Islam and Christianity.

Mohammed Rafat al-Tahtawi, the spokesman of state-run Al-Azhar Mosque, the country’s pre-eminent Islamic institution, announced on Al-Jazeera that he had resigned from his position to join the protesters.

“We’re calling on this to be the largest protest ever,” said Mahmoud Salem, a youth activist and blogger. “We are hoping it will be the last one.”

But Prime Minister Shafiq told Al-Arabiya that Mubarak’s departure was “unlikely.”

“Mubarak’s remaining as president is a source of security for the nation,” he said.

Trying to launch the transition with Mubarak still in place, Vice President Suleiman has offered negotiations with all political forces over constitutional changes needed to ensure a free vote ahead of September elections. Mubarak has said he will not run for re-election in the vote.

Suleiman said the dialogue invitation includes the protest leaders and regime’s top foe the Muslim Brotherhood. That was a significant point, suggesting the banned Islamic fundamentalist Brotherhood could be allowed an open political role in the post-Mubarak era.

But so far the protest factions have stuck to their condition that Mubarak step down before any negotiations on the constitution.