JERUSALEM — Prime Minister Olmert staved off a key coalition partner’s threat to bring down the government, giving him at least a few more months to pursue peace agreements with the Palestinian Arabs and Syria. But the last-minute deal could bring his political demise later this year.

In a pre-dawn agreement reached early today, Mr. Olmert’s Kadima Party told the Labor Party that it will hold primary elections by September 25. The primary is likely to oust Mr. Olmert as Kadima leader.

The Kadima pledge prompted Labor to rescind its support for a motion to dissolve the parliament, which had been expected to pass within hours.

The deal came a month after Mr. Olmert’s popularity was dealt a severe blow by an American businessman’s testimony in a corruption case against the Israeli leader. The businessman said he handed hundreds of thousands of dollars to Mr. Olmert in cash-stuffed envelopes, in part to finance a lavish lifestyle that included a penchant for fancy hotels and cigars.

Labor’s leader, the Defense Minister, Ehud Barak, threatened after the dramatic court testimony to force new elections unless Mr. Olmert resigned or agreed to Kadima primaries.

Today’s compromise allows both Messrs. Olmert and Barak to save face. Mr. Olmert can remain in office and keep his coalition intact, while Mr. Barak can tell supporters that he is forcing Kadima to change its leader.

Kadima officials say Mr. Olmert has not ruled out running in the party primary, hoping to clear his name after a cross-examination of the American businessman, Morris Talansky, slated for July 17. But opinion polls show Mr. Olmert to be extremely unpopular — both within the party and among the general public — and unlikely to win.

His likely successor would be the Foreign Minister, Tzipi Livni, or the Transportation Minister, Shaul Mofaz.

Ms. Livni, the chief peace negotiator with the Palestinian Arabs, is expected to push forward with American-backed efforts to reach a final peace deal before President Bush leaves office next January. The more hawkish Mr. Mofaz, a former military chief, would most likely slow down or break off the talks with both the Palestinian Arabs and Syria.

The Labor-Kadima deal, which was overwhelmingly approved by Kadima members later today, came after hours of intense talks overnight.

Although today’s vote was considered only a preliminary move under parliamentary rules, Mr. Olmert had threatened to fire any government minister who supported the motion.

Such a move would have left Mr. Olmert without a parliamentary majority and begun a process that was expected to bring elections by the end of the year. Currently, elections are scheduled in 2010.

Speaking on Israel Radio today, lawmakers Tzahi Hanegbi of Kadima and Eitan Cabel of Labor said the primary would be completed by September 25. But Mr. Cabel said he was concerned that Israel’s political and security volatility could upset the process and somehow leave Mr. Olmert in place.

A political analyst, Hanan Crystal, said the looming Kadima primaries will not prevent Mr. Olmert from pushing the international community for tougher action against Iran for its nuclear program. Israel believes Iran is pursuing nuclear weapons.

Mr. Olmert will also persist in efforts to resume official peace talks with Syria. The two nations are currently holding indirect talks through Turkish mediators. Israel also could launch a broad military campaign in Hamas-controlled Gaza if a fragile truce doesn’t hold.

“Ehud Olmert has what he wants, the big political exit he wanted, with Iran, with Syria and with Gaza,” Mr. Crystal told Israel Radio. “He is the legitimate prime minister for the entire summer.”