More than a year before the Sept. 11 attacks, a small, highly classified military intelligence unit identified Mohammed Atta and three other future hijackers as likely members of a cell of Al Qaeda operating in the United States, according to a former defense intelligence official and a Republican member of Congress. In the summer of 2000, the military team, known as Able Danger, prepared a chart that included visa photographs of the four men and recommended to the military’s Special Operations Command that the information be shared with the Federal Bureau of Investigation, the congressman, Representative Curt Weldon of Pennsylvania, and the former intelligence official said Monday. The recommendation was rejected and the information was not shared, they said, apparently at least in part because Mr. Atta, and the others were in the United States on valid entry visas. Under American law, United States citizens and green-card holders may not be singled out in intelligence-collection operations by the military or intelligence agencies. That protection does not extend to visa holders, but Mr. Weldon and the former intelligence official said it might have reinforced a sense of discomfort common before Sept. 11 about sharing intelligence information with a law enforcement agency.