JERUSALEM — Israel entered a monthslong season of political uncertainty Wednesday as Prime Minister Ehud Olmert's decision to resign in September cast the country into a leadership struggle that could complicate efforts to make peace with its neighbors.

Weakened by corruption scandals, Olmert announced he would not run in his centrist Kadima Party's Sept. 17 leadership primary and would step down afterward to give the new party chairman a chance to form a different government.

That means Israel, which has been negotiating with two Palestinian factions and Syria while grappling with how to confront Iran's nuclear ambitions, will be without effective leadership at least until October.

The power vacuum could last as late as February, overlapping the change of U.S. presidential administrations if a new Israeli government cannot be formed without general elections.

Olmert's decision was not unexpected. A shrewd, affable political survivor who once called himself "indestructible," the 62-year-old leader had battled longer than expected to cling to his job, even as he worked to engage some of Israel's adversaries in peace talks.

Those peace initiatives are likely to undergo fierce debate in the race to succeed him.

The leading candidates to head his party are Foreign Minister Tzipi Livni, Israel's chief negotiator with the Palestinian Authority, and Shaul Mofaz, a more hawkish former defense minister.

Former Prime Minister Benjamin Netanyahu, who leads in polls as Israel's most popular candidate, has voiced strong reservations about Israel's peace initiatives.

At stake are U.S.-backed negotiations between Israel and the Palestinian Authority over terms for a future Palestinian state. Israel also is talking indirectly with the more militant Palestinian group Hamas about a prisoner exchange and with Syria, through Turkish mediators, about a peace treaty.

Israel's succession struggle also comes amid sensitive discussions among its military and civilian leaders over how to confront what they believe is Iran's rush to develop a nuclear weapon. Israeli Defense Minister Ehud Barak, also a former prime minister, told U.S. officials in Washington this week that Israel will not rule out military action against Iran in the coming months.

Olmert will serve as a caretaker prime minister until his successor is chosen. He is likely to lean more heavily on his defense minister and Israel's military leaders in decisions about Iran, Israeli analysts said.

The prime minister said Wednesday that he would not "ease up" on peace efforts with Syria and the Palestinians "as long as I remain in office."

Uncertainty over Israel's political direction, however, could make it hard for him to close deals that have eluded Israeli leaders for decades or win their approval by parliament.

American and Palestinian officials insisted Olmert's departure would not slow the U.S.-backed peace talks. The latest round, held Wednesday in Washington, brought together Secretary of State Condoleezza Rice, Livni and chief Palestinian negotiator Ahmed Qurei.

"The Israelis will work out their own politics," U.S. State Department spokesman Sean McCormack told reporters. "We're going to look forward to working with all responsible Israeli leaders in the government, whether it's this government or some future government."

But few Israelis or Palestinians ever put much hope in the U.S.-sponsored negotiations, which have shown little visible progress since they began in November at Annapolis, Md. Serious differences remain over borders of a future Palestinian state and the future of Palestinian refugees. And Olmert said this week that there was no chance of achieving accord this year on rival claims to Jerusalem.

Aaron David Miller, a former U.S. negotiator in the Middle East, said Olmert's departure would reduce the prospects of a high-risk initiative to close the gap between the two sides. "No one believes that with this added uncertainty the chance of a real negotiation leading to binding agreements is possible," he said.

The Israeli leader's motives in pursuing negotiations have been viewed with growing suspicion as corruption allegations mounted against him and his popularity rating crashed into the single digits.

Many Israelis and Arabs believed Olmert's overtures "were meant to give an impression that he deserves to stay in office so he can make peace," said Ghassan Khatib, a former Palestinian Authority Cabinet official.

Olmert was in political trouble almost from the start of his tenure, pursued by police investigators looking into earlier corruption cases and damaged by an inconclusive 34-day war against Lebanon's Hezbollah guerrillas two summers ago that many Israelis took as a defeat.

He took over in January 2006 after Prime Minister Ariel Sharon's debilitating stroke and was elected to a four-year term two months later. He had served in public office since 1973, as a member of parliament, mayor of Jerusalem and trade minister in Sharon's government.