WASHINGTON, Dec. 21 - An instructor at a Minnesota flight school warned the F.B.I. in August of his suspicion that a student who was later identified as a part of Osama bin Laden's terror network might be planning to use a commercial plane loaded with fuel as a weapon, a member of Congress and other officials said today.
The officials, who were briefed by the school, said the instructor warned the Federal Bureau of Investigation in urgent tones about the terrorist threat posed by the student, Zacarias Moussaoui. Mr. Moussaoui, a French citizen of Morrocan descent, was indicted last week on charges of conspiring in the Sept. 11 terror attacks.
Representative James L. Oberstar of Minnesota, who received the briefing and is the ranking Democrat on the House Transportation Committee, said the instructor called the bureau several times to find someone in authority who seemed willing to act on the information.
Mr. Oberstar said the instructor's warnings could not have been more blunt. The representative said, "He told them, `Do you realize that a 747 loaded with fuel can be used as a bomb?' "
Mr. Oberstar described the instructor as "an American hero" whose actions resulted in Mr. Moussaoui's arrest and might have prevented another suicide hijacking.
Congressional officials said the account by the school, the Pan Am International Flight Academy in Eagan, outside Minneapolis, raised new questions about why the Federal Bureau of Investigation and other agencies did not prevent the hijackings.
Officials said the Arizona branch of the school alerted the Federal Aviation Administration earlier this year after finding that a student spoke little English. The Saudi student, Hani Hanjour, has been described as being at the controls of the plane that crashed into the Pentagon.
The instructor in Minnesota has not been identified. But Congressional officials said he was a former military pilot who grew suspicious after encounters in which Mr. Moussaoui was belligerent and evasive about his background and because he was so adamant about learning to fly a 747 jumbo jet despite his clear incompetence as a pilot.
Mr. Moussaoui, 33, was arrested in August on immigration charges. But despite the urging of the school and federal agents in Minnesota and despite a warning from the French that Mr. Moussaoui was linked to Muslim extremists, F.B.I. headquarters here resisted a broader investigation until after Sept. 11. Last week, he became the first person indicted for involvement in the events of Sept. 11, charged with conspiring with Mr. bin Laden and Al Qaeda. Mr. Moussaoui faces the death penalty.
Some federal law enforcement agents said they believed that Mr. Moussaoui was intended to be the 20th hijacker.
Until now, the bureau and the flight school have been unwilling to provide details on what raised suspicions about Mr. Moussaoui. But several weeks ago, the school offered to brief a handful of House members and their aides who were involved in aviation. Two lawmakers were from Minnesota, Mr. Oberstar and Martin Sabo, a fellow Democrat, and they first discussed the briefings today in The Star Tribune in Minneapolis.
In interviews today, Mr. Oberstar and a spokesman for Mr. Sabo said the lawmakers were alarmed by what they heard. They withheld information from the public about the briefings until this week, they said, because they did not want to interfere with the inquiry that led to Mr. Moussaoui's indictment.
Mr. Sabo, ranking Democrat on the Appropriations Subcommittee on Transportation, was traveling today. His chief of staff, Michael S. Erlandson, who was at the briefing, said the flight academy's account was scary. "The Pan Am people," Mr. Erlandson said, "are heroes who worked very diligently to make themselves heard at the F.B.I."
He said Mr. Moussaoui raised the suspicions in a first encounter, when he told the instructor that he was from France but refused to converse in French with the instructor, who also spoke it. The suspicions grew, Mr. Erlandson said, when Mr. Moussaoui repeatedly proved himself incapable of understanding basic flying techniques but still insisted on learning how to fly a 747, the largest commercial jet.
Mr. Erlandson said the flight school had arranged the briefings. "They called up," he said, "and said that they were constituents and that they had an almost unbelievable story they would like to share."
A spokeswoman for the academy did not return calls for comment. Spokesmen for the Federal Bureau of Investigation and Federal Aviation Administration also had no comment.
Mr. Oberstar said he was also troubled by the F.A.A. response to the Phoenix instructors' concerns about Mr. Hanjour, who enrolled speaking little English, which is required for all commercial pilots. According to the school, it contacted the F.A.A. this year to ask what it should to do with Mr. Hanjour. Mr. Oberstar said the agency offered the services of one of its employees to help tutor Mr. Hanjour.