The government is investigating a report from medical authorities that one of the Sept. 11 hijackers was treated three months before the terror attacks for a lesion that could have been caused by exposure to anthrax, U.S. officials said Saturday.

The information is contained in a memorandum prepared by experts at the Johns Hopkins Center for Civilian Biodefense Strategies who studied a Florida doctor's treatment of hijacker Ahmed Ibrahim A. Al Haznawi, the officials said. The memo concluded that anthrax was the most likely diagnosis for the man, said Tim Parsons, a spokesman for Johns Hopkins University's school of public health.

Al Haznawi, a possible Saudi national, was one of the hijackers on United Airlines Flight 93, which crashed in rural Pennsylvania.

Exposure to anthrax by one of the hijackers would raise the possibility they had handled anthrax and could have had a role in the bioterror attacks last fall that killed five people. The four anthrax-tainted letters that have been recovered, each dated "09-11-01," were postmarked Sept. 18 and Oct. 9.

The New York Times reported Saturday that Al Haznawi was treated for a lesion on his leg in June by Dr. Christos Tsonas, who cleaned the sore and prescribed an antibiotic. The man said he developed the sore after bumping into a suitcase. After the Sept. 11 and bioterror attacks, Tsonas concluded that Al Haznawi's lesion was consistent with exposure to anthrax, the Times said.

Tsonas, an emergency room doctor at Holy Cross Hospital in Fort Lauderdale, Fla., said in a statement Saturday that the Times article "was, in my opinion, well researched and factually correct."

He said he could provide "no further information than that already available" and declined further comment. Hospital spokeswoman Maria Soldani said the hospital was cooperating with authorities and would not discuss the matter at their request.

Doctors at the Johns Hopkins center also reviewed the man's treatment and concluded he probably had been exposed to anthrax, Parsons said.

A senior intelligence official, speaking on condition of anonymity, said CIA Director George Tenet had received the Johns Hopkins memo and that government officials were looking into it. "No one is dismissive of it," the official said. "No one's ruling anything out."

But Assistant FBI Director John Collingwood played down the possible anthrax connection.

"This was fully investigated and widely vetted among multiple agencies several months ago," he said in a written statement. "Exhaustive testing did not support that anthrax was present anywhere the hijackers had been. While we always welcome new information, nothing new has, in fact, developed."

Five people died from the inhaled form of anthrax after tainted letters were sent last fall to people in Florida, New York and Washington, D.C. Dozens of other people contracted the skin form of the disease, which is more easily treated.

FBI Director Robert Mueller said earlier this month that U.S. investigators have not identified which of the nation's research laboratories may have been the source of the anthrax. Nor has the bureau narrowed the case to a single suspect or group of suspects.