U.S. officials are now casting serious doubt on whether a hostage-taker photographed in 1979 after the U.S. Embassy seizure in Tehran is Iran's new president-elect.

Despite the general resemblance between President-elect Mahmoud Ahmadinejad and the 1979 image of a bearded young Iranian escorting a blindfolded American hostage, an initial study of the photograph by U.S. officials revealed several key facial differences, especially in the ears, angle of the eyebrows, pattern of the beard, cheeks and forehead area above the eyebrows, the officials said.

"After a comparison between this individual -- the president-elect -- and the hostage-taker, the thinking is now that it's not the same person," said one of several U.S. officials familiar with the review, who would speak only on the condition of anonymity because the investigation is sensitive and ongoing. "The discrepancies are so many that I don't know who could say that's the same dude."

The case is far from closed, however, and still has the potential to revive a quarter-century-old crisis. The Bush administration now wants an accounting of whether Ahmadinejad played any role in the holding of 52 Americans captive, said other U.S. officials familiar with the administration's deliberations.

Ahmadinejad was a university student in Tehran when the walled U.S. Embassy compound was seized by a coalition of students to protest the Carter administration's decision to allow the ousted shah of Iran to enter the United States for medical treatment. Initial findings that Ahmadinejad may not be the youth in the picture do not necessarily mean he was not involved in the takeover, U.S. officials said yesterday.

The dispute was sparked when at least half a dozen American hostages said they recognized Ahmadinejad after his stunning election upset last weekend brought him into the international limelight. Some of the former U.S. military personnel said that he was in charge of their harsh interrogations and that they have vivid recollections of long hours spent with him.

"The pictures are one piece of the puzzle," said a senior State Department official also familiar with the investigation, who would only speak anonymously because of the diplomatic sensitivities. "The fact of the matter is that American hostages have said that they recognize this guy, so we take that very seriously."

"The fact is that 52 Americans were held 444 days, and we don't take that lightly and we want to document that as fully as possible to determine what we're dealing with in Tehran," he said.

Ahmadinejad's office vehemently denied the assertions, as did three of the top ringleaders of the embassy takeover who today are all reformers opposed to the hard-line president-elect. A relative newcomer to politics, Ahmadinejad was unknown both at home and abroad until he was appointed Tehran's mayor in 2003. His victory marks the final phase of a political takeover by Iranian ultraconservatives, who swept the parliamentary elections last year and the municipal elections the year before in major turnovers from an eight-year period of reform.

Other hostages have told the State Department that they have no recollection of Ahmadinejad. "I don't recognize him," said John W. Limbert, a former embassy political officer who is president of the American Foreign Service Association. "I don't remember these guys' faces very well. They didn't introduce themselves to us."

In an interview Thursday, one of the original ringleaders said Ahmadinejad may have been among the hundreds of students who passed through the U.S. Embassy as the crisis dragged on or were affiliated with the student coalition. But three of the student planners asserted that they have no memory of Iran's president-elect taking a major role in the seizure.

State Department spokesman Sean McCormack said yesterday that various government agencies are still collecting the facts.

"People are searching through all the information at their disposal, searching through files. . . . I expect that we will reach out to people who were actually there, who were hostages," he told reporters. "I don't believe that has happened yet, but I know there is the intention to do so."

Any evidence that the new Iranian president, who is expected to be inaugurated in August, was complicit in the U.S. Embassy takeover could have an impact on a range of U.S. policies and actions, including access to international institutions, U.S. officials said. At least two Iranian presidents have attended the annual opening of the U.N. General Assembly in New York.

An American hostage was presented by his Iranian captors in 1979. Some ex-hostages say Iran's new leader was one of their captors, third from right.Iranian President-elect Mahmoud Ahmadinejad is shown in portrait released by his campaign Web site.