o the moment of truth has arrived. For the past four years, the Israeli prime minister, Ariel Sharon, and President Bush have used the very existence of Yasir Arafat to justify their abandonment of the peace process. The Palestinians, for their part, have used Israel's and America's intractability to continue their own self-destructive policy of intifada, and Mr. Arafat's immovable presence as the all-purpose explanation for everything from internal corruption to suicide bombers.

Now Mr. Arafat is gone, and so are the excuses.

In Mr. Arafat's place is a Palestinian leadership that says it wants a smooth and democratic transfer of power and is prepared to talk if Mr. Sharon wants to.

Chances like this aren't likely to come again in Mr. Sharon's lifetime. If he wants to avoid Mr. Arafat's fate - dying as a former hero turned obstacle to his people's progress - he has to take advantage of it. As Israel's greatest friend, the United States must do everything it can to make that happen. Unfortunately, Bush officials are tap-dancing, spouting the same tired excuses that America can't do anything to restart the road map to peace until Palestinian extremists end their violence against Israel, and until Palestine has a leader America can trust.

Mr. Arafat was a democratically elected Arab leader, and it's incumbent on the United States to do everything possible to make sure that his successor is chosen by a process that's as open, honest and transparent as possible. The Palestinians have already asked the United States for help in holding elections within 60 days. Obviously, that aid should be given - and the administration should also be willing to regard the winner who emerges from the voting with the same tolerance and presumption of legitimacy that it is preparing to give to the victors in the deeply imperfect balloting that will be going on in Iraq in January.

American leadership in this area has never before been more crucial, and Mr. Bush cannot fail again. He should make four simple statements: We have an opportunity. We have a plan. We have a goal. Let's talk.

First on the list is Mr. Sharon's plan to withdraw the Jewish settlements from the Gaza Strip. Benjamin Netanyahu and the Israeli far right, who are fervently opposed to the Gaza withdrawal plan, will now undoubtedly say that Israel no longer needs this unilateral plan because resuming the peace process means everything is back on the table. That urge should be stamped down, and quickly. The key to progress is certainly not going backward.

In Gaza, the Palestinians, for their part, will face one of the first big tests of their post-Arafat leadership. The fact that there are many historical reasons why the Palestine Liberation Organization's administration has been both corrupt and inept at management cannot be used as an excuse for the future. If the United States is obligated to push the Israelis into extending the withdrawal process to the West Bank, the Palestinians are obliged to demonstrate that if they get their own country, they will run it responsibly.

A year ago, Israelis and Palestinians of good will got together in Geneva and hammered out a peaceful settlement that, while totally unofficial, called for the steps that have long been recognized as the only true hope for a permanent peace. The plan calls for two neighboring states with two capitals in Jerusalem, the evacuation of most Jewish settlements and the incorporation of the rest into Israel in exchange for an equivalent amount of land for Palestine. It also calls for a limit, to be set by Israel, on the number of Palestinian refugees who can settle in Israel, and compensation or resettlement for the rest.

This is the chance for peace that has been approached, then squandered, over and over, as one party or the other lost the necessary nerve. This time, everyone will have the same old opportunities to fail. There are bound to be attacks by Palestinian extremists, which will allow Mr. Sharon to dig in his heels and say he will negotiate only if the new leaders crack down on radicals. Mr. Arafat's successors will be under extraordinary pressure to follow Mr. Arafat's path by talking to the West about peace while allowing the terrorists to dictate actions at home.

But Israel can help shore up the credibility of moderate reformers by beginning a total freeze on settlements and beginning to address their calls to withdraw from the West Bank and Gaza. What better way to empower moderate leaders than by giving them something that Israel refused to give Yasir Arafat?

Windows of opportunity don't open often, particularly in this part of the world. Keeping this window open will take some tough choices, but the reward could put us back on the road to a real peace.