Sharon said it would be "difficult" for Likud to remain the ruling party if party members reject his plan to withdraw from all Gaza Strip settlements and four West Bank enclaves.
"I feel there is a great danger that we will be dragged into elections, as a result of which the Likud could be pushed out of power," Sharon said on Channel 10 TV.
He also told Channel Two that he is determined to bring peace and security, "and therefore I will fight to try to advance" the plan.
In recent weeks, supporters of the pullout maintained an edge, but surveys this week -- including one broadcast yesterday on Channel 10 -- pointed to a flip-flop.
"We are worried," a Sharon adviser, Lior Horev, acknowledged yesterday.
The Channel 10 survey, conducted by Marketwatch, said that of the 500 Likud members polled, 48 percent were opposed, 37 percent in favor, and 15 percent remained undecided. No margin of error was given.
A Yediot Ahronot poll showed 47 percent of Likud members would vote against the plan, with 40.5 percent in favor. The same poll two weeks ago found 54 percent in favor of the plan. Yesterday's poll questioned 804 respondents, and had a margin of error of 4.5 percentage points.
Other polls yesterday showed a narrower margin, with Maariv showing 45 against and 42 in favor of the plan. No margin of error was given for the poll of 474 Likud members.
Opponents of the plan -- among them ultra-Orthodox settlers who normally observe the Jewish Sabbath by not driving, working, or using electricity -- were expected to campaign throughout the weekend.
Settlers have waged an intense campaign, holding demonstrations, putting up posters across the country, and visiting the homes of Likud members.
They have argued that a pullout would hurt Israel's security and reward Palestinian terror attacks. Opponents also plan to send volunteers to polling stations for last-minute lobbying.
Sharon has communicated with voters mostly through the media. He also has worked the phones, calling dozens of Likud activists.
The referendum marks the first time a vote is being held in Israel on an issue that has divided the nation for decades: whether to give up land captured in the 1967 Middle East war.
