President Bush savored his Rose Garden moment Wednesday, celebrating the beginning of a new Mideast peace push with smiling Israeli and Palestinian leaders. It might be a long time until he gets another such opportunity.

The old bugaboos of Mideast peacemaking remain unsolved and there are fresh obstacles that will make Bush's job as shepherd even harder. The U.S. role in new negotiations is deliberately vague, but Bush and his envoys are expected to prod and monitor both sides and intervene directly if talks founder.

"I wouldn't be standing here if I didn't believe that peace was possible," Bush said, with nods to Israeli Prime Minister Ehud Olmert and Palestinian President Mahmoud Abbas beside him, "and they wouldn't be here either if they didn't think peace was possible."

The few minutes in the Rose Garden marked the third day in a row that Bush rang the bell to begin talks aimed at establishing an independent Palestinian homeland. The agreement for the talks — which skirts the hard details — was the centerpiece of a U.S.-sponsored peace conference Tuesday in Annapolis, Md.

Pleased with the outcome of the 44-nation session, the Bush administration decided to bring the two leaders together again at the White House a day later.

The Rose Garden appearance before the cameras felt rushed, and only Bush looked to be truly enjoying himself. Abbas and Olmert, the leaders who will be asked to cede land, take risks and drop long-standing demands, made no public statements there.

"One thing I've assured both gentlemen is that the United States will be actively engaged in the process," Bush said. "We will use our power to help you as you come up with the necessary decisions to lay out a Palestinian state that will live side by side in peace with Israel."

Few of the issues that Abbas' and Olmert's negotiators are tackling at the outset lend themselves to intervention by an American president, but the U.S. pledged to arbitrate both sides' compliance with past, unfulfilled promises.

U.S. officials also say that although Bush laid out no bridging proposals of his own at Tuesday's session, that kind of direct negotiating role could become necessary.

Secretary of State Condoleezza Rice is expected to continue her nearly monthly visits to the region, aided by retired Marine Corps Gen. James L. Jones, a new security envoy she named Wednesday. The announcement was timed to show momentum, even before the first formal bargaining sessions on Dec. 12. No U.S. envoy is expected to attend that initial meeting.

Three main disputes have sunk previous efforts at peace: the borders of an eventual Palestinian state, the status of Jerusalem and its contested holy sites and the rights of Palestinians to return to land inside present-day Israel.

A hard-won joint agreement read out by Bush on Tuesday made no attempt to settle any of those looming questions. It doesn't even mention them.

Other good reasons abound why a serious run now at the six-decade conflict seems doomed, and politically crass.

At the head of the effort are weak or unpopular leaders consumed with domestic political problems. The Palestinians are divided into two armed camps, and the clock is running out on Bush's presidency.

But there is an alternate argument that now is a rare moment that cannot be missed, and all the important parties know it. Inherent in seizing this moment is the risk that failure will set the goal of peace farther back than it is now, but all sides seem to have concluded that they have more to lose by doing nothing.

"When the conditions are right, like they are in this case, in the Palestinian and Israeli issue, it's worth it to go for peace," Bush told The Associated Press in an interview Tuesday.

For Olmert, that means that he is seeking a peace deal despite opposition on the political right and left at home, personified by hungry rivals waiting to see if he slips up. There is also a corruption investigation and his persistent unpopularity resulting from perceived mistakes in last year's war in Lebanon.

One jaundiced view in Israel has Olmert going through the motions of peace because an ongoing negotiating process may provide some job security.

Olmert may also have concluded that he should make a deal before Bush leaves office because the current U.S. administration is more likely to sympathize with Israel's worries that any concessions make a tiny country more vulnerable to hostile neighbors.

Abbas needs progress to show he is the legitimate leader of all Palestinians, sealing his primacy over Hamas militants who stormed to control in the Gaza Strip in June. Abbas also has a friendly relationship with Olmert, whom he views as a fellow pragmatist. Palestinians may get a better deal from Olmert than they would from Olmert's possible successors.

Bush and Rice have their own reasons for putting on the heat now. They include fear of a rising Iran and Islamic extremism sown by the festering Palestinian problem and the drumbeat of irritation from Arab allies over the perception that Bush has abdicated peacemaking responsibilities until now.

Analysts said it is hard to set specific markers for U.S. involvement going forward, but added that the world will be watching for signs that Bush is invested in the outcome after seven years of a mostly hands-off approach.

"The bar to convincing people of your seriousness is higher because of your previous behavior," said The Century Foundation Mideast analyst Daniel Levy, a former Israeli peace negotiator.