Sharon said before the party's referendum that new elections were likely if his party voted no. Exit polls conducted by three Israeli television stations indicated that about 60 percent voted against the plan, with about 40 percent in favor. Official results were expected early today.
The prime minister had vowed to carry out his plan to abandon all Jewish settlements and withdraw all Israeli troops in the Gaza Strip, as well as to close four isolated settlements in the West Bank. Sharon could still present the plan to his Cabinet and to Israel's parliament, where the outcome is uncertain.
Before the polls closed, he raised the possibility of conducting a national referendum on his plan to unilaterally disengage Israelis from Palestinians.
Sharon said in a statement last night that he would study the results of yesterday's vote and meet in the coming days with Cabinet ministers, Likud officials and representatives of the other parties in his coalition government.
"The people of Israel didn't elect me to sit four years with my hands folded," he said in the statement. "I was elected in order to find a way to bring the people peace, security and quiet. I intend to lead the state of Israel according to the best of my conscience."
Over the weekend, Sharon sought to turn the referendum into a personal vote of confidence, saying: "You can't be for me and against my plan."
Israeli authorities said two Palestinian gunmen ambushed a station wagon driven by Tali Hatuel, 34, who was eight months' pregnant, and her four children, ages 2 to 11, and shot everyone inside as they drove on Kissufim Road, which links the Gush Katif settlement to Israel.
The gunmen were identified as members of the Popular Resistance Committee, an umbrella group representing several Palestinian militant groups, including Hamas and Islamic Jihad. The Israeli army said that since September 2000, 10 civilians and five soldiers have been killed on the road.
Israeli helicopters retaliated by firing missiles at a 14-story apartment building in Gaza that housed a Hamas radio station. Israeli gunships later fired missiles at a car in the West Bank city of Nablus, killing four Palestinians that the Israeli army identified as "senior terrorists" of the Aqsa Martyrs Brigades.
Asher Mivtzary, a resident of the Kfar Darom settlement in Gaza, said the killing of the Hatuel family proves that Sharon's plan is tantamount to a surrender to Palestinian violence.
"The tragedy shows that Arabs think that this plan meant that they had won the war," he said. "The vote shows that people in Israel understand that the way to peace is not to retreat in the middle of a war."
Mivtzary, who has lived in the settlement for 12 years and raised his eight children there, said the vote by Likud members reaffirms Israel's commitment to the settlements as a part of the vision for a Greater Israel.
"We love Sharon, but we don't want to leave our homes," he said.
Palestinian officials said they hope the defeat of Sharon's plan will force the Israelis back to the negotiating table. While they support an Israeli withdrawal from Gaza, Palestinian officials object strongly to Israel taking unilateral actions and to the Bush administration's endorsement of the Sharon approach.
Supporters of Sharon's plan complained that those voting in yesterday's referendum were not representative of Israelis at large. About 40 percent of Likud's 193,190 members cast ballots. And the party's members represent only a small fraction of the overall population, which according to opinion polls overwhelmingly supports a withdrawal from Gaza.