That outcome seemed ever more elusive.

An Egyptian official complained that the US was pressing for Mubarak’s swift departure even as President Barack Obama publicly urges an orderly transition.

“There is a clear contradiction between an orderly process of transition and the insistence that this process be rushed,” said the official, who was speaking for his government but said the government would not allow his name to be associated with the statement.

“Now means now,” White House spokesman Robert Gibbs said, and he declared anew that continued aid to Egypt would be influenced by the Egyptian government’s response to the crisis.

While the US has not directly called for Mubarak to resign, the protesters’ chief demand, Gibbs was echoing Obama’s public call one night earlier for an immediate and orderly transition to democracy in Egypt. Instead the images on TV were of a brutal clash between protesters and Mubarak supporters.

“If any of the violence is instigated by the government, it should stop immediately,” Gibbs said, while declining to speculate whether the Egyptian government was in fact behind the violence. Protesters contended plainclothes police were among the pro-Mubarak groups.

The White House had attempted to nudge Mubarak to the exits, dispatching former US Ambassador Frank Wisner as a special envoy to deliver the message to him. By Wednesday, Wisner was on his way back to the United States.

A senior US official, speaking on condition of anonymity due to the delicacy of the matter, suggested Wisner had been seeking specific pledges from Mubarak beyond just a promise not to stand for re-election. The official would not elaborate, but the administration has made no secret that it wants the state of emergency lifted and would prefer to see Mubarak’s son, Gamal, not try to succeed his father. Mubarak mentioned neither in his address Tuesday night.

The White House said it had had no indication that such violence was in the offing when Obama and Mubarak had spoken frankly Tuesday night. The Egyptian president announced on television that he would not seek re-election in September, but protesters want him out now.

With Mubarak’s grip on his country in doubt, Obama’s team is evaluating scenarios of what may come next. But the conflict underscores the limits of the American president’s power to shape the outcome.

For example, State Department spokesman P.J. Crowley acknowledged the Muslim Brotherhood is “a fact of life in Egypt” and might play a role in the nation’s transition.

US officials haven’t met with members of the organization though they’ve spoken to other opposition groups, Crowley said.

He also said that Secretary of State Hillary Rodham Clinton had spoken with Egypt’s new vice president to urge an investigation into attacks on protesters. She apparently was the first Cabinet-level official to reach out to Omar Suleiman, a longtime confidant of the US.

Clinton urged the government of Egypt to “hold accountable those who were responsible for violent acts,” in a statement from the office of the State Department’s spokesman released late Wednesday.

Clinton also “expressed hope that both the government and the opposition would seize the opportunity, starting immediately,” created by Suleiman’s call for “a broad dialogue with representatives of Egypt’s opposition parties,” the statement also said.

Obama has spelled out what Egypt’s transition to free elections should look like, but he has refused to say whether Mubarak should be in charge all the while. Obama has spoken to Mubarak and telephoned fellow world leaders to try to bolster stability in the region, but he cannot stop violence in the streets of Cairo. To the degree Obama has spelled out consequences of inaction to Mubarak, the White House will not say much publicly.

Obama also is trying to find a balance between responding appropriately to events without being sucked up in hour-by-hour reaction. Gibbs said history was being made, and “this is not all going to be wrapped up in a matter of hours. It’s going to take some time.”

Thousands of supporters and opponents of Mubarak battled in Cairo’s main square on Wednesday, throwing stones, bottles and firebombs as soldiers stood by without intervening. The fighting started when several thousand Mubarak supporters, including some riding horses and camels and wielding whips, attacked anti-government protesters.