However, a defeat could trigger a major political crisis, including a Cabinet reshuffle, a split in Likud or even early elections. Sharon would be weakened politically by a defeat in his own party, but he is not expected to resign.

Analysts say that even though polls give referendum opponents a strong lead, the race is still open. Much depends on how many of Likud's 193,000 members turn out, with a strong showing expected to help Sharon.

The voting began as scheduled at 8 a.m. Sunday. Official results were expected Monday.

Under Sharon's plan of "unilateral disengagement," Israel would withdraw from the Gaza Strip and evacuate some 7,500 settlers, take down four small West Bank settlements and complete construction of a West Bank separation barrier by the end of 2005. Sharon argues that this would give Israel defensible borders and reduce friction with the Palestinians in the absence of a final peace deal.

Opponents, who say an Israeli withdrawal will be viewed as a victory by Palestinian militants, accuse Sharon of betraying the settlers, his erstwhile constituents. For decades, Sharon was the foremost champion of settlement expansion, responsible for establishing many of the communities he now plans to remove.

In Gaza, an 8-year-old Palestinian boy was killed Saturday and 12 Palestinians were wounded, 10 of them minors, by army fire near Israeli settlements, hospital officials said. The army said soldiers fired in response to an anti-tank missile and several firebombs. Two teens got too close to a settlement, the army said.

In the West Bank, a 22-year-old Palestinian died of wounds suffered during a clash with Israeli forces, doctors said. Palestinians said he was a bystander.

Referendum opponents have run a tight campaign, visiting tens of thousands of Likud members in their homes. Thousands of Gaza settlers spent the weekend with relatives in Israel for a final campaign of persuasion in synagogues Saturday and at polling stations Sunday.

Sharon placed phone calls to Likud activists after the Jewish Sabbath ended at sundown Saturday. However, he had less than two hours since he was not expected to call Likud members at home after the start of the Euroleague basketball championship game.

With defeat appearing likely, critics said Sharon underestimated his opponents and did not campaign hard enough. In calling the referendum about a month ago, Sharon was confident his popularity in the party would translate into easy victory.