A loss in the Likud Central Committee vote could force new elections and jeopardize the Gaza withdrawal — a centerpiece of efforts to restart peace talks with the Palestinians in the wake of Yasser Arafat's death.
But a win would add a partner solidly in favor of the Gaza pullout and resumption of peace negotiations. Some in Labor oppose joining Sharon, but party leader Shimon Peres is strongly in favor.
Results were expected around midnight local time (around 5 p.m. EST).
Also Thursday, an Israeli soldier went on trial in a military court on charges of.
Soldiers fired at the girl, Iyman Hams, as she approached a military observation post near the Rafah refugee camp in the Gaza Strip on Oct. 5. The soldiers said they thought she was planting a bomb. The girl's family said she was on her way to school.
According to the five-count indictment, the officer approached the girl after she was shot and fired two rounds at her body from close range in an outlawed practice known as "verifying the kill." He walked away, turned around and shot her again, the indictment charged.
The soldier, who has not been identified, has been charged with two counts of illegally using his weapon, and one count each of obstruction of justice, conduct unbecoming an officer and improper use of authority.
The 3,000-member Likud party already voted in August against inviting Labor to join the government. But after Sharon fired a key coalition partner for voting against his budget on Dec. 1, his coalition is more tenuous than ever. He has warned that the choice is now Labor or elections.
A lengthy electoral campaign would almost certainly delay if not completely thwart his plan to withdraw from Gaza and four West Bank settlements next year.
Members of the Likud body trickled in to the Tel Aviv convention center to cast their votes. There was no debate — party leaders said the issues are clear and have been discussed at length for months.
Worried about a low turnout that would favor his opponents, Sharon made a rare appeal to his backers to vote.
"I want to say that we are standing before great opportunities and events that could be historical, and I won't let anything or anyone harm the opportunity of the state of Israel to take advantage of these opportunities," he told Army Radio.
His efforts at turning out the vote appeared to have worked: After eight hours, only 40 percent of Likud members had voted, but the percentage had climbed to 54 an hour later.
Sharon defied his party and his own ideology when he first presented his plan to remove all 21 Jewish settlements from Gaza and four small ones from the West Bank a year ago.
For decades, Sharon was the patron of the settlements, enabling their construction and expansion, and his Likud hotly opposed conceding any land to the Palestinians or creation of a Palestinian state.
Over the past year, however, Sharon has changed his policy, but most of his party refuses to go along.
Sharon says the Gaza settlements, with 8,200 Jews living among more than a million Palestinians, are untenable and must be removed. That would give Israel a better chance to retain its main settlement blocs in the West Bank, where most of the 236,000 settlers there live, he believes, and it would also head off international peace efforts unfavorable to Israel.
Opponents reject evacuating any settlements as a matter of principle and also warn that an Israeli pullout from Gaza would lead to international pressure to withdraw from the West Bank.
The Likud rank and file overwhelmingly voted against the withdrawal in a party referendum on May 2. Sharon ignored the vote and pressed ahead.
This time, however, Sharon has run out of political elbow room. After dismissing all his coalition partners in spats over the withdrawal plan and the state budget, he has only his Likud in the government.
Likud has 40 seats in the 120-member parliament, but up to half the Likud members oppose the Gaza withdrawal. Without Labor's 21 votes and at least one smaller ultra-Orthodox Jewish party for insurance against the Likud rebels, Sharon could lose a no-confidence vote at any time and be voted out of office.
Arafat's death on Nov. 11 has opened new possibilities for a breakthrough in long deadlocked Mideast peace talks, since Israel and the United States considered him an obstacle.
But a lull in fighting after his death ended in recent days. On Thursday, an Israeli aircraft fired a missile at a car carrying Palestinian militants in southern Gaza, wounding four men. One was Jamal Abu Samhadana, one of the two Gaza commanders of the Popular Resistance Committees, an umbrella group of militant factions.
None of the injuries was reported to be life-threatening.
"It was a cowardly assassination attempt ... but they have survived," Abu Abeer, a spokesman for the PRC, told the Jerusalem Post.
Israel has said it would refrain from carrying out offensive operations — unless it was attacked or had information of an imminent attack — in an effort to ensure calm in the run-up to Jan. 9 Palestinian elections.
Before daybreak on Thursday, Israeli soldiers opened fire on five suspicious Palestinians near the Gaza border with Egypt, killing two and wounding a third, the army said.
The soldiers suspected the Palestinians were either planting bombs in the area or smuggling weapons over the border, the army said.
Overnight, the army said it shot at four figures crawling toward the Egyptian border late Wednesday, hitting two. Palestinian medics said they recovered four bodies.