The already stalled U.S. road map for a settlement between Israel and the Palestinians hangs in the balance with the resignation of Prime Minister Mahmoud Abbas (search), whose support was considered essential to any prospect of success.

Stunned Bush administration officials withheld immediate comment Saturday after Abbas submitted his resignation, the apparent loser in a power struggle with Yasser Arafat (search).

State Department (search) spokesman said only that "our representatives in the region are in touch with the parties." A senior State Department official had no comment but made clear the administration is not certain that Abbas' rocky tenure as prime minister is over.

Several hours after Abbas acted, a Palestinian lawmaker said Arafat, the leader of the Palestinian Authority who appointed Abbas last spring to mollify the Bush administration, had accepted the resignation.

But Dennis Ross, who spent 12 years as former President Clinton's top Middle East mediator and also worked in the region under President Bush, said the possibility remains that Abbas could be persuaded to change his mind.

"I wouldn't totally rule it out, but I think we have to understand that he's not going to go back under the same circumstances," said Ross. "And I think the broader lesson is, if you can't get him to go back, you're not going to get anybody else to, either."

Abbas' appointment was a condition for implementation of the so-called road map, pushed by the United States in conjunction with the United Nations, the European Union and Russia.

President Bush, saying Arafat was involved in terrorism and not a fit partner for peacemaking, demanded that he appoint a prime minister to handle day-to-day affairs of the authority and handle peace negotiations. Arafat chose Abbas, a longtime ally and fellow founder of the Palestine Liberation Organization's Fatah faction, but they have been at odds almost from the time he was appointed.

Abbas' decision to quit apparently caught the administration by surprise. Only two days ago, White House spokesman Scott McClellan said President Bush was concerned about the Abbas-Arafat rivalry.

But reflecting a hands-off U.S. policy, the spokesman said that was best left to the Palestinians. "I will point out the importance of all parties working together to meet their obligations under the road map," McClellan said.

Still, the administration never shrank from scorning Arafat publicly. Secretary of State Colin Powell saying a few days ago that he was not interested in anything the longtime Palestinian leader might have to say about peacemaking.

Powell insisted on Friday, however, that some progress was being made.

While most Arab and European governments still recognize Arafat's authority, Bush shunned him and courted Abbas. In a Friday speech at George Washington University, Powell praised Abbas for trying to consolidate Palestinian security forces and curb corruption.

"This is the way to rebuild the Palestinian society and the Palestinian economy on a sound basis to benefit all Palestinians," Powell said. "This is the way to a Palestinian state."

Yet Abbas has shied away from repeated U.S. demands that he dismantle Palestinian extremist groups on the West Bank and Gaza and has limited his efforts to persuasion. Most anything more substantial, he has insisted, would lead to civil war.

Nonetheless, the Bush administration maintained a drumbeat of demands that the terror structure be dismantled. Otherwise, Powell insisted repeatedly that Palestinian aspirations for a state would not be fulfilled and peacemaking hopes would "go over the cliff."

Clearly the administration and its road map partners were at a loss on how to keep alive the plan for establishing a Palestinian state by 2005 to live side-by-side at peace with Israel.

A senior State Department official, Assistant Secretary John S. Wolf, shuttled between the region in getting instructions in Washington, trying to bolster Palestinian security to stop further attacks on Israel. Deputy Secretary of State Richard Armitage tentatively has scheduled a trip to the area next week, but it was unclear whether the weekend's events would affect the plans.