Israeli Prime Minister Ariel Sharon (search) has called for a referendum within his Likud Party (search) on his plan to unilaterally withdraw from the Gaza Strip (search) and parts of the West Bank (search), Israeli officials said Friday.

Sharon's request, lodged with the party Thursday night, means the vote will be held within the next three weeks under the ruling party's bylaws.

Sharon had initially said he would not call for the referendum until after he returned from a trip next week to Washington, where he will meet with President Bush in an effort to garner American backing for his plan.

He decided to speed up the timetable to keep the momentum going from his Washington trip and to make it harder for the opposition within his hard-line party to organize, political sources said.

Sharon has said he will honor the outcome of the referendum. A recent poll showed a slim majority of Likud members supporting his proposal.

The Palestinians fear Sharon is giving up Gaza to pre-empt a negotiated settlement and tighten his hold on much of the West Bank. However, they also said they welcome any withdrawal.

Though the Gaza pullout is not expected for up to a year, the prospect has led to a flurry of meetings among Palestinian factions and speculation about how strong the Islamic militant groups' influence would be afterward.

Palestinian Foreign Minister Nabil Shaath said Thursday an Israeli withdrawal from Gaza could clear the way for long-delayed elections that might include the militant Hamas group.

"We hope this (withdrawal) will pave the road for a Palestinian general election with participation with Hamas," he told The Associated Press.

Shaath, who meets with senior U.S. administration officials later this month, told Israel Radio the Palestinians will demand the United States do "nothing that will pre-empt a permanent settlement, neither on borders nor refugees or anything."

Opponents of Sharon's withdrawal plan complained the Likud vote was being rushed and party members would not have enough time to study the plan's details.

"I think that what made the prime minister's advisers pull this political trick is their own fear of our (opposition) campaign," Likud parliamentarian Gilad Erdan told Israel Radio. "They understand that with every day that passes, Likud members study the ramifications of the program further and more and more of them oppose it."

Sharon adviser Raanan Gissin said the prime minister was trying to move on the plan before the situation in the region further deteriorates.

Sharon wants "to do it as quickly as possible to get it out of the way," Gissin said of the referendum. "He's determined to move along with this."

Israel and the United States have warned Hamas may try to take over Gaza after an Israeli pullout.

Palestinians have had only one general election since the Palestinian Authority was set up in 1994. Hamas boycotted the 1996 voting, refusing to recognize the Palestinian Authority, set up in an interim peace accord with Israel. Hamas does not accept a Jewish state in the Middle East.

Hamas leader Abdel Aziz Rantisi did not rule out participation in possible new elections. "Hamas is looking for a real partnership, not a cosmetic one," he told reporters in Gaza at a Hamas rally late Thursday.

Hamas has claimed responsibility for most of the homicide bombings that have killed more than 450 Israelis during 31/2 years of conflict. On March 22, Israel assassinated the leader and founder of Hamas, Sheik Ahmed Yassin, and Hamas pledged revenge.

Gissin said Hamas is a terrorist group that should not be allowed a governing role. "This is another effort by the Palestinian Authority to bypass the requirement to fight terrorism," he told The Associated Press. "This is not Hamas joining the PA. This is the PA joining Hamas."

The stalled U.S.-backed "road map" peace plan requires the Palestinians to dismantle violent groups like Hamas, but Palestinian leaders have avoided a confrontation, fearing a civil war. Israel has also ignored its initial "road map" obligation to stop settlement construction.

"Our view is that, far from being welcomed into any partnership or cooperation, Hamas should be ostracized and disempowered as an organization," U.S. State Department spokesman Adam Ereli said this week.