JERUSALEM — Ehud Olmert is hoping his upcoming visit to Washington, his first as Israeli prime minister, will bring U.S. backing for a major Israeli withdrawal from the West Bank — yet Olmert doesn’t even have unqualified support from his own government for a unilateral move.

Olmert’s main coalition partner, defense minister and Labor Party leader, Amir Peretz, insists that Olmert first fully explore the possibility of a negotiated settlement with the Palestinians.

The situation is further complicated by differences on the Palestinian side. While the radical Hamas government rules out peace talks with Israel, Palestinian Authority President Mahmoud Abbas, leader of the more moderate Fatah movement, has been imploring Olmert to open negotiations with him and warning that unilateral moves by Israel could lead to a violent conflagration.

The upshot is likely to be a coordinated, two-pronged American-Israeli policy: exploring peace talks with Abbas while simultaneously drawing up detailed plans for a unilateral withdrawal that will go into high gear if talks fail.

Olmert begins his diplomatic dealings with the Bush administration convinced that there’s no genuine peace partner on the Palestinian side. In his view, Hamas has ruled itself out and Abbas is too weak to deliver.

Olmert probably will tell the Americans that while he is willing to explore the Abbas channel, it’s almost certain to fail. Since Israel can’t continue to be sucked into an occupation it doesn’t want, he’ll argue, Israel and the United States should start tackling the enormously complex unilateral option without delay.

Olmert leaves for the United States on Sunday. On Monday he meets Secretary of State Condoleezza Rice and Defense Secretary Donald Rumsfeld, then meets with President Bush on Tuesday, possibly for several hours. On Wednesday, Olmert is due to address a joint session of Congress.

Aides say Olmert will seek agreement on the following general principles in his Washington talks:

* The time to be allotted to peace talks with Abbas before they can be declared ineffective;

* American readiness in principle to back a policy shift to unilateral withdrawal if it becomes apparent that peace talks are irredeemably deadlocked;

* An American commitment to mobilize international support for any unilateral Israeli moves;

* American readiness to negotiate with Israel over where its permanent borders should run, and to recognize them if agreement is reached.

The basis for future Israeli-American border negotiations will be Bush’s April 2004 letter to then-Prime Minister Ariel Sharon. Bush wrote that it would be “unrealistic” to expect Israel to return to the pre-1967 boundaries, and implied American support for the retention of “already existing major Israeli population centers,” a reference to large West Bank settlement blocs.

In the months ahead, the two sides will need to translate these general ideas into specifics on the ground. Olmert hopes that if the United States agrees on a line, it will recognize it as a permanent border and get the international community to do the same. That would make it much easier for Olmert to galvanize domestic support for withdrawal.

But there’s a catch: When Bush wrote his letter, Yasser Arafat was still leading the Palestinian Authority and was seen as blocking all avenues to peace. Abbas, Arafat’s successor, seems genuinely committed to peacemaking — and, if at all possible, the United States would much prefer to see borders agreed upon in negotiations between Israel and the Palestinians.

Complicating matters for the prime minister, Peretz also favors a negotiated settlement. Like Olmert, he believes Israel may ultimately have to make unilateral moves, but, unlike the prime minister, he thinks a channel to Abbas could be productive.

In closed sessions with top Defense Ministry officials, Peretz called for an early resumption of contacts with the Palestinian Authority and said talks with Abbas should be given every chance. In the event of a breakthrough, he argued that Abbas would be able to bypass Hamas by putting any agreement with Israel to a Palestinian referendum.

Olmert was not impressed. How would he make the case for unilateralism in the United States when his defense minister was prioritizing talks with the Palestinians, he asked in a tense meeting with Peretz last week.

“Only I have the authority to make policy,” Olmert reportedly said.

There also has been movement on the Palestinian side toward re-engagement with Israel. A document negotiated between two jailed but influential leaders, Marwan Barghouti of Fatah and Sheik Abdel Halek Natshe of Hamas, has been hailed by both Hamas and Fatah officials as a basis for “national dialogue” that could lead to a compromise on policy toward Israel.

In contrast to the official Hamas position, the document appears to accept the principle of a Palestinian state alongside Israel and endorses all previous Palestinian-Israeli agreements — though recognition of Israel is only implied, not explicit.

It also calls for the formation of a national unity government and for the inclusion of Hamas in the PLO umbrella organization. Such moves could give more credibility to a negotiation between Israel and Abbas, who is not only the P.A. president but also PLO chairman.

In a speech Monday marking the anniversary of the Palestinian “Nakba” — the “catastrophe” that accompanied the creation of the State of Israel — Abbas underlined his determination to revive peace talks. He urged Palestinians to stop their “futile rocket attacks” on Israel and called on Israel to drop its claim that there’s no Palestinian partner.

“The partner exists, and we extend our hand to you in peace,” he declared.

The Palestinian quandary is clear. If they don’t get into significant negotiations with Israel soon, they could find themselves having to accept borders and other realities over which they have no say.

Jordan’s King Abdullah put it succinctly: The Palestinians, he said in early May, have just two years to reach an agreement with Israel.

“I fear if this short time elapses and we don’t reach a settlement, that there will be nothing left for the Palestinians to negotiate over,” he told , the Dubai-based Arabic TV news channel Al-Arabiya.

The countdown begins with Olmert’s Washington visit: One way or another, it will start laying the groundwork for new borders between Israel and the Palestinians.