Israeli Prime Minister Ariel Sharon is to visit Washington this week, where he hopes to win the backing of President George Bush for his plan to pull out of Gaza and parts of the West Bank. Observers say the outcome of the White House talks will influence Mr. Sharon's chances of winning a referendum of his Likud Party later this month.

Mr. Sharon is to meet Wednesday with Mr. Bush to discuss his plan to unilaterally pull troops and Jewish settlements out of the Gaza Strip. Under the plan, Israel would also dismantle four Jewish settlements in the West Bank.

Mr. Sharon is hoping to get written guarantees of support from Mr. Bush that will help him win a majority of his ruling Likud Party for the plan. The Likud is set to hold an internal ballot of its 200,000 members on Mr. Sharon's proposals on April 29.

Should he emerge victorious, Mr. Sharon intends to put the plan before his Cabinet on May 2 and then to the Israeli parliament for approval the following day.

Observers say Mr. Sharon's prospects depend on how much support he can win from the U.S. administration.

Israeli media report that Mr. Sharon and Mr. Bush are expected to exchange letters that will include both the details of Mr. Sharon's plan and what Washington can be expected to provide in terms of support. Mr. Sharon's demands include effective U.S. recognition of Israel's right to annex some Jewish settlement blocs in the West Bank.

He is also seeking Mr. Bush's rejection of the Palestinians' long-standing claim for the right of return of Palestinian refugees to areas that are now part of Israel.