jerusalem | With the Labor leadership primary less than two weeks away, it’s becoming increasingly clear that the party’s next leader will decide the future of Ehud Olmert’s government.

Four of the five candidates are threatening to pull Labor out of the coalition with Olmert’s Kadima Party. If that happens, it would almost certainly bring down the government and spark early elections.

Only current Labor Party leader Amir Peretz, 55, is prepared to go on serving unconditionally in an Olmert-led government.

Both front-runners — Ami Ayalon, the former Shin Bet security services chief, and former Prime Minister Ehud Barak — say they will take Labor out of the coalition unless Olmert steps down or sets a date for early elections.

With Ayalon and Barak running neck and neck, the race is heating up. And the stakes are high: Given the nation’s current leadership vacuum, either man could quickly become a serious candidate for prime minister once he is installed as Labor chief.

It was the youngest candidate, Ophir Pines-Paz, 45, who focused the race around the issue of leaving the coalition. For months he has been arguing that Labor cannot remain in an Olmert-led government and retain credibility as a more caring and less corrupt governing alternative.

In the wake of the Winograd Commission’s scathing report on Olmert’s conduct of last summer’s Lebanon war, Pines-Paz held a 48-hour strike outside the prime minister’s official Jerusalem residence, demanding that he resign. Labor, Pines-Paz said, could not possibly go on serving in a government headed by such a tarnished leader.

Former Mossad Chief Dani Yatom, 62, whom polls show in last place, took a similar position. Ayalon, who initially favored staying in an Olmert-led government, changed his mind and now says he will lead Labor into the opposition.

The experienced Barak adopted a more nuanced stance. In a makeshift press conference at Kibbutz Sdot Yam last week he demanded that Olmert resign — but Barak also said he would be prepared to serve as defense minister in an Olmert-led government for a short, transitional period until new elections.

Labor’s Central Committee was scheduled to meet Friday, May 18 in Tel Aviv to vote on the future of its alliance with Kadima.

Meanwhile, the race between Ayalon and Barak is heating up. In what Israeli newspapers dubbed “the war of the generals,” Amiram Levine, a former head of the Israel Defense Forces’ Northern Command, tore into Barak, questioning his integrity and accusing him of “throwing people who help him to the dogs” when he no longer needs them.

Labor’s choice, Levine wrote, was between “leadership that was rotten and corrupt” (Barak) or “straight, genuine and serious” (Ayalon). The Barak camp accused Ayalon of getting Levine to write what he did.

With five candidates, one would need 40 percent of the vote to win outright in the first round. A runoff is likely in mid-June, probably between Ayalon and Barak.

Ayalon, who commanded the Navy from 1992 to 1996, headed and rebuilt the Shin Bet after its failure to prevent the assassination of Yitzhak Rabin in 1995. He has a master’s degree in business from Harvard and a reputation for integrity and straight talk.

In 2003, Ayalon launched the “Peoples’ Voice” with Palestinian academic Sari Nusseibeh, persuading hundreds of thousands of Israelis and Palestinians to sign onto a six-point peace deal.

Ayalon’s Achilles heel, though, is his lack of political experience: He has never held a ministerial post.

Barak’s great advantage is his experience as IDF chief of staff, prime minister, defense minister, foreign minister and interior minister. His weakness is his failure as prime minister from 1999 to 2001, when peace talks with both Syria and the Palestinians proved fruitless, the intifada began and Barak was forced to run in an early election that he lost in a landslide to Ariel Sharon.

But both men have a political gravitas that could pave the way for a serious bid for the premiership. For the first time in years, Labor could be about to get a credible challenger for national leadership.