Israeli Prime Minister Ehud Olmert’s highly successful visit to the United States has already resulted in important gains for Israel.

Mr. Olmert sought American backing for his unilateral disengagement plan, the platform on which he was elected and formed his coalition government. As the prime minister explained to me when I met with him in his office several weeks ago, the essence of the Olmert plan is that should Israel confirm the absence of a viable Palestinian negotiating partner, the Jewish state will unilaterally redeploy to new lines of its own choosing.

In real terms, this would involve a significant withdrawal from much of the west bank, and from the overwhelming majority of the Palestinian population there, to lines defined by the route of the security barrier being built to separate Palestinian areas from Israeli ones.

These lines will not be the 1967 lines, and Mr. Olmert was counting on the commitments laid out in President Bush’s April 14, ‘004 letter to Ariel Sharon that in the event that new borders are drawn, account will be taken of the new demographic realities on the ground. In simple English, this means that President Bush supports the proposition that some of the major settlement blocs outside the Green Line 1967 border will remain part of Israel.

On this score, Mr. Bush did not disappoint, specifically reaffirming the views expressed in the April ‘004 letter. Mr. Bush lent a virtual endorsement to the Olmert plan, calling it a "bold" idea.

That endorsement was virtual rather than absolute because the United States has not formally abandoned the idea that any resolution of the Israel-Palestinian conflict should be based on terms negotiated between the two sides. Mr. Olmert was therefore under pressure to delay implementing his unilateral plan until after some decent interval during which a last ditch effort would be made to engage Palestinian moderates around Palestinian Authority Chairman Mahmoud Abbas.

Last month, Mr. Olmert told an international delegation of mayors visiting Israel under the auspices of the annual Jerusalem Mayors Conference that he would give the Palestinian negotiation option the next half-year before proceeding with his plan. He repeated this commitment during his talks last week with President Bush and the U.S. Congress.

Behind the scenes, the debate in Jerusalem was whether the government would use this pause through the end of ‘006 to make a serious effort to "build-up" Chairman Abbas.

In theory, everyone agrees that to exchange territory for an internationally recognized negotiated peace settlement is preferable to a unilateral redeployment. After all, why give something for nothing?

The problem is that Chairman Abbas already has a long record of weakness and failure, as well as that a shattered and divided Fatah movement that has thus far made no attempts to address the causes of its precipitous fall from power.

Moreover, the agreed-upon formula for proceeding with bilateral negotiations — the "road map" for Middle East Peace — requires that Chairman Abbas unify the Palestinian militias, disarm the terrorists, and uproot their infrastructure before moving on to further diplomatic steps. Mr. Abbas has clearly been unable, or unwilling, to fulfill his end of this bargain.

But political life is full of moves and countermoves. It was always possible that as Israel’s unilateralist policy — strongly opposed by Palestinian factions — picked up momentum it would trigger a change in the Palestinian position.

Last Thursday, Chairman Abbas finally made a move, calling Hamas’ bluff by announcing that if Hamas did not accept the prisoners’ plan for a two-state solution along the 1967 lines by the next Sunday, he would appeal over their heads to the Palestinian voters in the form of a referendum in July.

Chairman Abbas was basing himself on a recently published joint declaration by Fatah and Hamas prisoners held in an Israel jail.

This took Hamas officials by surprise and also required follow-up steps from Israeli leaders who announced the transfer of a limited amount of weapons and ammunition to Chairman Abbas’ presidential guard.

Assuming Hamas refuses to back down, and if (and this is a big if) Chairman Abbas follows through with a referendum, his position will probably carry the day. That would create an entirely new landscape, full of new dangers and opportunities for Israel. The opportunity is for a chance to exploit the differences between the "no recognition" Hamas line and the "ambivalent recognition" implied in the prisoners’ plan. The danger is that the international community will be so relieved to see a change in the Palestinian position that it will ignore the facts that the prisoners’ plan is no peace plan and promotes the right of return of Palestinian refugees to Israel proper as well as "armed resistance" in the west bank.

Despite its limitations, the referendum that Chairman Abbas has announced has one commanding virtue to recommend it, and to some this may be superior to all the objections: the fact that it is opposed by Hamas. If, a month down the road, a vote was called, with the advocates of a two-state solution arrayed on the one side and the opponents of it on the other, and the vote carried, it could make a significant, even historic contribution toward a solution, the literal meaning of the wording notwithstanding.

What is important to keep in mind is that, however long in the planning, Chairman Abbas’ decision to finally stand up to Hamas came right after Prime Minister Olmert’s unilateral plans received a warm Washington welcome, and a day after Congress voted to tighten restrictions against any economic help for a Hamas-run Palestinian Authority.

American and Israel had to say "no’ to get even the semblance of a Palestinian "yes."