The American-led Annapolis peace conference achieved the minimum — a pledge by Israel and the Palestinians to begin immediate negotiations with a goal of reaching a peace treaty by the end of 2008.

We are encouraged that President Bush, best known for waging war in Iraq, has finally accepted the challenge of peacemaker. An agreement would give Palestinians their long-promised homeland and help make Israel more secure. It could also diminish the appeal of Islamic extremists and begin to repair America’s battered reputation in the Muslim world.

Still, the difficulty of reaching an accord before Mr. Bush leaves office cannot be overstated. Yesterday’s joint statement, which was vaguer than we had hoped, is a reminder of just how difficult. While the two sides said their talks would be aimed at concluding a treaty that deals with all “core issues,” they couldn’t agree on naming them and how they might be addressed. For the record, they are: the future of Jerusalem, the fate of refugees, the borders of a Palestinian state and guaranteeing Israel’s security.

The parties also pledged to fulfill their obligations under the 2003 “roadmap,” including ending Israeli settlements and Palestinian violence. That is a restatement of past, mostly broken, promises. The announcement that an American-led group would be formed to monitor and judge progress could help make the process more credible. The joint statement speaks of “continuous” negotiations, but that doesn’t necessarily mean nonstop — which is what a deal almost certainly would take.

Prime Minister Ehud Olmert of Israel and Palestinian President Mahmoud Abbas are both weak leaders who need maximum backing from the United States, Arab leaders and other major countries to make serious compromises.

It is encouraging that 49 countries and international organizations, including Saudi Arabia and Syria, came to Annapolis, Md., yesterday to bless the effort. The refusal of Prince Saud al-Faisal, the Saudi foreign minister, to shake hands with Mr. Olmert was a worrying reminder of how far many Arab countries still have to go. The prince did clap politely after Mr. Olmert’s speech. The Syrian representative did not.

The guest list was notable for those left off: Iran and its allies, the militant factions Hamas and Hezbollah. A credible negotiation may help persuade those violent spoilers to rethink their obstructionism or persuade their backers to rethink their allegiances.

In his opening speech, President Bush, assured Israel and the Palestinians that “America will do everything in our power to support their quest for peace.”

We hope that he means it — and that he makes that clear to all those White House aides who keep extolling the virtues of not getting too involved.

If there is any hope of pulling this off, Mr. Bush and his secretary of state, Condoleezza Rice, will have to invest their time, their reputation and their best arm-twisting, including offering bridging proposals to nudge both sides beyond their long-fixed positions. There’s no chance at all if Mr. Bush goes back to the sidelines.