Zalmay Khalilzad, the plainspoken dealmaker and Republican insider who has won praise and criticism for attempts to broker Sunni political participation in Iraq's fragile government, is likely to quit his post as U.S. ambassador in Baghdad in the coming months, a senior Bush administration official said Monday.

As the midterm elections approached in the United States, Khalilzad has been a public face of Bush administration attempts to project both willingness to change strategy or tactics in an unpopular war and solidarity with the increasingly fractious Shiite-led government of Prime Minister Nouri al-Maliki.

Khalilzad's departure has been rumored for months, but he has not turned in his resignation, the State Department official said. The official spoke on condition of anonymity because neither the White House nor Khalilzad has announced any personnel changes. Khalilzad could leave as soon as the end of this year, but is more likely to remain in his post through the spring, the official said.

"He doesn't want to stay there forever and there are ongoing discussions about when he will finish his time, but there is no definite date," the official said.

Other U.S. officials have said Khalilzad will probably return to an academic or private sector job in the United States. His replacement in Baghdad may be Ryan Crocker, a senior career diplomat who is currently U.S. ambassador to Pakistan, those officials said. Crocker was a top U.S. representative in Baghdad for several months in 2003, shortly after the U.S.-led invasion that toppled Saddam Hussein.

Khalilzad is an Afghan-born Sunni Muslim who was seen as a go-between among Iraq's political and sectarian factions when named to the Baghdad post in April 2005. Initially criticized by some Shiites for showing what they called favoritism to the Sunni minority, Khalilzad has more recently been a target of Sunni criticism that the United States is not doing enough to protect Sunnis from Shiite reprisals and death squads.

National Intelligence Director John Negroponte, during a Baghdad visit on Friday, told al-Maliki that Khalilzad would leave about the first of the year and replaced by Crocker, according to two top aides to the Iraqi leader. The aides spoke on condition of anonymity because they are not authorized to release information.

Negroponte was Khalilzad's predecessor as ambassador in Baghdad. Khalilzad had been the Bush administration's ambassador to Afghanistan after the fall of the Taliban. A White House favorite whom Bush calls by his nickname "Zal," Khalilzad worked in the Republican administrations of Ronald Reagan and George H.W. Bush.

Al-Maliki snubbed Khalilzad two weeks ago, when the ambassador held a press conference to announce that Iraqi leaders had agreed to develop a timeline by the end of the year for progress in stabilizing the country, only to be contradicted by al-Maliki hours later.

Last week Khalilzad and U.S. military commanders agreed to lift a U.S. security cordon around a Shiite slum in Baghdad after meeting with al-Maliki. Sunnis claimed that al-Maliki asked to lift the cordon on orders from anti-American Shiite cleric Muqtada al-Sadr, an important base of al-Maliki's support.

Aides to the prime minister have said flatly that he hopes to expand his authority by playing on American voter discontent and White House reluctance to open a public fight just before the elections.