WASHINGTON - Zalmay Khalilzad, who was President George W. Bush's ambassador to Afghanistan, could assume a powerful, unelected position inside the Afghan government under a plan he is discussing with Hamid Karzai, the Afghan president, according to senior American and Afghan officials.

Former U.S. ambassador to the U.N. Zalmay Khalilzad speaks to the media after a meeting of the Security Council to discuss the conflict between Russian and Georgia at United Nations headquarters in New York in this August 11, 2008 file photo. (REUTERS/Keith Bedford) Mr. Khalilzad, an American citizen who was born in Afghanistan, had considered challenging Mr. Karzai for the presidency in elections scheduled for this summer.

But Mr. Khalilzad missed the May 8 filing deadline, and the American and Afghan officials say that he has been talking with Mr. Karzai for several weeks about taking on a job that the two have described as the chief executive officer of Afghanistan.

Such an alliance would benefit Mr. Karzai by co-opting a potential rival. For its part, the White House has made no secret of its growing disenchantment with Mr. Karzai, and some Afghanistan experts said that enlisting Mr. Khalilzad would have the virtue of bringing a strong, competent leader into an increasingly dysfunctional Afghan government.

The position would allow Mr. Khalilzad to serve as "a prime minister, except not prime minister because he wouldn't be responsible to a parliamentary system," a senior Obama administration official said. Taking the unelected position would also allow Mr. Khalilzad to keep his American citizenship.

Administration officials insisted that the United States was not behind the idea of enlisting Mr. Khalilzad to serve in the Afghan government, and they gave no further details on what his duties might be.

They said that Mr. Karzai had sought out Mr. Khalilzad, but that the idea of enlisting a chief executive had also been raised by Gordon Brown, the British prime minister.

American and British officials expressed concern that any belief that the West was behind the plan would harm its chances inside Afghanistan. They spoke on the condition of anonymity because they were not authorized to discuss the matter publicly.

"This has the makings of a really bad movie," said Teresita C. Schaffer, a South Asia expert at the Center for Strategic and International Studies in Washington.

"The idea of having an American as a major senior official of Afghanistan is a very risky one both for the Afghan government and the person in question."

But she added: "Whoever is going to run Afghanistan will have to have both feet on the ground there, and I know Zal has intimate knowledge of the country and was involved to a degree that was virtually unheard of for an ambassador."

Mr. Khalilzad met with Mr. Karzai about the job when Mr. Karzai visited Washington two weeks ago, and they discussed the proposal then.

Mr. Khalilzad then flew to Kabul, the country's capital, several days ago to continue talks with Mr. Karzai, whose re-election campaign comes at a time when security in Afghanistan is deteriorating.

During his visit to Washington, Mr. Karzai also outlined his plan to Secretary of State Hillary Rodham Clinton and Richard C. Holbrooke, the special representative to the region, the officials said.

Administration officials say that President Obama, Mrs. Clinton and Mr. Holbrooke all told Mr. Karzai that it was up to him and Mr. Khalilzad to decide whether to proceed.

A plan that puts Mr. Khalilzad near the top of a Karzai government would provide the Obama administration with a strong conduit to push American interests in Afghanistan, particularly in cracking down on corruption and the drug trade, which American officials say has helped to fuel the resurgence of the Taliban.

While Mr. Khalilzad served in the Bush administration - including as ambassador to Iraq and the United Nations - he has maintained ties with the Obama administration as well, and has twice been to the State Department to meet with Mr. Holbrooke.

Mr. Khalilzad could not be reached for comment on Monday.

Mr. Karzai has already successfully defused the candidacies of other potential rivals for the presidency.

One of them, Gul Agha Shirzai, the popular governor of Nangarhar Province, announced after a four-hour meeting with Mr. Karzai that he was pulling out of the presidential race.

Another, Muhammad Qasim Fahim, a former warlord who later became defense minister, was identified by Mr. Karzai as one of two vice-presidential running mates, in a move widely interpreted as an attempt to bolster Mr. Karzai's standing among former mujahedeen parties.

Kai Eide, the United Nations special representative to Afghanistan, criticized the choice of Mr. Fahim because of human rights concerns.

It remains unclear whether Mr. Karzai and Mr. Khalilzad can strike a deal on an alliance, the American and Afghan officials said.

Several of Mr. Karzai's own ministers have opposed such a pact, they said, and it is not certain whether Mr. Karzai remains willing to bring Mr. Khalilzad aboard now that the filing deadline for presidential candidates has passed.

Mr. Karzai and Mr. Khalilzad have had a long and sometimes bumpy relationship. They worked closely when Mr. Khalilzad was ambassador to Afghanistan, from 2003 to 2005, and Mr. Karzai, the new president of a fledgling democracy, was viewed as a darling of the West.

But as the United States and Britain have become increasingly disenchanted with Mr. Karzai amid widespread corruption allegations, the two men have also put some distance between themselves, which expanded further as Mr. Khalilzad began to make plans to run against Mr. Karzai for president.

While he was working for the Bush administration, Mr. Khalilzad often brushed up against other officials, including Secretary of State Condoleezza Rice.

He got in trouble for appearing on a panel with Iran's foreign minister without getting permission from the White House first. And he annoyed State Department officials when he arranged to meet in Dubai with Asif Ali Zardari to talk about Mr. Zardari's bid for the presidency of Pakistan, just when the United States was trying to convince Pakistanis that America was not interfering in their internal politics.