Polls published on Sunday just before the referendum reaffirmed previous surveys indicating a majority opposed his move to evacuate all Jewish settlers in Gaza and a few in the West Bank.
His plan also entails holding onto larger West Bank settlement blocs containing the majority of Jews on territory Israel occupied in the 1967 Middle East war.
Likud has traditionally opposed giving up any land captured in war with Arabs and the settlers lobbied hard against the "Disengagement Plan", staking out Israeli intersections, hoisting anti-withdrawal signs and meeting Likud members.
Sharon, long the godfather of the settlement movement, says
his plan would reduce Israelis' exposure to "Palestinian violence" while retaining territory deemed strategically vital.
Nationwide opinion polls indicate a majority of Israelis support
withdrawal from Gaza. But Sharon's Likud opponents and far-right coalition partners say that leaving Gaza would "reward terror".
That argument resonated among those Israelis who believe a
unilateral pullout in 2000 from Lebanon, where troops were under constant resistance attack, encouraged Palestinians to begin their uprising later that year.
Sharon's aides made clear that even if he lost Sunday's vote, he would present his plan to his cabinet and to parliament, where the chances of approval are higher. In the event of defeat, Sharon could also call a national referendum.
Urging 'yes vote'
Defence Minister Shaul Mofaz urged the Likud to accept the
plan. He said on Israel Radio that it was "good for Israel" and
could be carried out by the end of 2005.
"The proposal should win a majority and be implemented as quickly as possible because no matter what, we will implement this plan whether it is approved today or in the future," Mofaz said on Israel Army Radio.
Shaul Mofaz is urging the Likud
to accept the Gaza pullout
Sharon tried to rally support by warning the right-wing party that voting down the proposal could jeopardise Israel's vital ties with the United States, weaken the party's grip on
power and force new elections.
Failing to sway Likud's rank-and-file would deal a strong blow to Sharon, already embroiled in a corruption scandal that threatens to topple him. Israel's attorney general is to decide soon whether to indict Sharon, who denies any wrongdoing.
But the 76-year-old former general, prime minister since
2001, stopped short of threatening to resign in a series of
last-ditch appeals on television to Likud's 193,000 members to
show their confidence in him and back the proposal.
Polls published on Sunday, however, continued to reflect majority opposition to his plan.
One survey found 47.5% against the pullout and 44% in favour, while a second predicted 49% would vote it down and only 41% would approve it.
"The proposal should win a majority and be implemented as quickly as possible because no matter what, we will implement this plan whether it is approved today or in the future"
About 7500 Israelis live in the Gaza Strip, home to 1.3 million Palestinians. There are 200,000 settlers in the West Bank, which has a Palestinian population of 2.3 million.
Under Sharon's scheme, Israel would abandon all 21 small settlements in Gaza and four of the 120 it put in the West Bank.
He said the pullout would improve Israel's security and
pledged to retain control for ever over larger West Bank
settlements, a move Palestinians regard as a land grab.
Voting at 168 polling stations started at 8am (05:00 GMT)
and is to continue until 10pm (19:00 GMT), with initial
results expected to be released around midnight.