United Nations ? The United States, Russia, the European Union and the United Nations gave qualified backing to Israeli Prime Minister Ariel Sharon’s imperiled Gaza withdrawal plan Tuesday, calling it a “rare moment of opportunity” in the hamstrung search for Middle East peace.

But in a bow to Arab concerns, the diplomatic “Quartet” said key issues, such as the shape of a future Palestinian state and the fate of Palestinian refugees, should be decided in negotiations with Israel, not by unilateral Israeli moves.

The meeting had been intended to boost to Sharon’s withdrawal plan, which U.S. officials see as a way to reinvigorate Middle East peace negotiations.

Instead, it occurred two days after Sharon’s conservative Likud Party voted overwhelmingly to reject the plan, leaving its status uncertain.

The meeting came “at a time when hope is in short supply,” acknowledged Foreign Minister Brian Cowen of Ireland, the EU’s president.

Sharon’s plan calls for an Israeli withdrawal from the occupied Gaza Strip and some settlements on the West Bank. Sharon has said he would try to enact it, although it may have to be modified. Some Israeli officials have talked about a partial withdrawal from Gaza instead.

But the Mideast Quartet, in a statement read by U.N. Secretary-General Kofi Annan, said Sharon’s initiative “must bring about a full Israeli withdrawal and complete end of occupation in Gaza.”

Arab and Palestinian leaders were angered last month when President Bush, in a meeting and exchange of letters with Sharon, stated that in his view Israel would be able to keep some large settlements in the West Bank and that Palestinian refugees wouldn’t be able to return home as part of a peace deal.

Arab leaders viewed the deal as a U.S.-Israeli attempt to impose a solution on the Middle East conflict, cutting out the Palestinians.

King Abdullah of Jordan, who meets Bush on Thursday after postponing his visit in protest, has asked the White House for his own letter of assurance that issues such as settlements and refugees, among the most emotional between Israelis and Palestinians, will be negotiated as part of an eventual peace deal.

U.S. officials confirmed Tuesday that no such letter is planned. Bush, they said, already has reiterated his view that the issues ultimately must be negotiated by the two sides.

Secretary of State Colin Powell said the Quartet statement on the issue “should provide that sort of assurance to the Arab world and to Palestinians.”

“And we are in conversation with our other Arab friends to see what assurances and comments they may need from us to make sure that they know that the president has not abandoned them, has not abandoned the hope for the creation of a Palestinian state,” Powell said.