Former Premier Ehud Barak edged out Ami Ayalon, a former chief of Israel's navy and internal security service, 36 percent to 31 percent in Monday's voting. While the victory marked an important milestone in Barak's attempt to make a political comeback, he fell short of the 40 percent threshold needed for an outright victory.
Supporters of the current Labor leader, Defense Minister Amir Peretz, will play a key role in deciding who comes out ahead. Israel's flawed war in Lebanon last summer sealed Peretz's defeat in Monday's race, but he still won 22 percent of the vote, coming in third. Peretz was keeping mum Tuesday on whether he'd back either candidate, but planned consultations with allies throughout the day.
In other developments:
The crucial Labor Party race has implications far beyond the party itself.
"I think many people understand that we are, in fact, not just voting on the future of the Labor Party but to a very large extent on the future leadership of the state of Israel," Ayalon said as he cast his ballot on Monday.
Labor has served as the junior partner in Olmert's year-old government. Its next leader is expected to shake up that alliance.
Both Barak and Ayalon have called for Olmert's resignation in the wake of a highly critical government report on his performance during the Lebanon war. It's unclear, however, how quickly they would work for his ouster, because remaining in government — least temporarily — could benefit both men.
Ayalon, 61, could use the time to build his popularity inside Labor and with the general public. The 65-year-old Barak, unseated as premier following eruption of the Palestinian uprising seven years ago, would like a senior Cabinet post to rehabilitate his tarnished image.
Barak has said he would serve temporarily in an Olmert government, while also pushing for early elections. Olmert was elected last year to a four-year term.
Ayalon has promised to lead the centrist Labor out of its partnership with Olmert if the prime minister's Kadima Party doesn't choose a new leader.
Both Ayalon and Barak could face a tough time leading their party out of the government, however. Many senior Labor officials want to hold on to power, or are afraid the party would lose in new general elections.
Opinion polls forecast the Likud Party, led by former Prime Minister Benjamin Netanyahu, would win handily if elections were held today. Likud takes a hard line against concessions to the Palestinians, whereas both Barak and Ayalon are willing to cede large chunks of land in a final peace deal.
Should the 19-member Labor faction bolt the government, Olmert could try to avert elections by propping up his government with religious or hawkish parties opposed to making concessions to the Palestinians.
Alternatively, with Labor demanding that he step down, the embattled Olmert might face new pressure within Kadima to comply.
Olmert spokeswoman Miri Eisin said the prime minister's office wouldn't comment on the Labor race.
The two contenders did not discuss the race's results or issue statements Tuesday.
Opinion polls published last week forecast Ayalon would defeat Barak in a head-to-head contest. But those same polls also put Ayalon ahead in Monday's vote.
Radio talk shows discussed Peretz's kingmaker role.
"If Amir Peretz doesn't get involved, Ehud Barak will win the primaries," political commentator Hanan Crystal told Israel Radio.
At the same time, Crystal said, "I estimate that it will be hard to impose his will on his people, so even if he tries, the race will be tight."
For Barak, Monday's win was an important step in his attempted political comeback.
He spent nearly six years in political exile after he was crushed by Ariel Sharon in a 2001 election, following a short and stormy premiership that collapsed after failed efforts at making peace with Syria and the Palestinians.
Peretz had said he would leave the defense job regardless of the vote. His party successor is expected to seek the defense minister's position.