A military intelligence team repeatedly contacted the F.B.I. in 2000 to warn about the existence of an American-based terrorist cell that included the ringleader of the Sept. 11 attacks, according to a veteran Army intelligence officer who said he had now decided to risk his career by discussing the information publicly. The officer, Lt. Col. Anthony Shaffer, said military lawyers later blocked the team from sharing any of its information with the F.B.I.

Colonel Shaffer said in an interview that the small, highly classified intelligence program known as Able Danger had identified by name the terrorist ringleader, Mohammed Atta, as well three of the other future hijackers by mid-2000, and had tried to arrange a meeting that summer with agents of the F.B.I.'s Washington field office to share the information.

But he said military lawyers forced members of the intelligence program to cancel three scheduled meetings with the F.B.I. at the last minute, which left the bureau without information that Colonel Shaffer said might have led to Mr. Atta and the other terrorists while the Sept. 11 plot was still being planned.
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The Defense Department did not dispute the account from Colonel Shaffer, a 42-year-old native of Kansas City, Mo., who is the first military officer associated with the so-called data-mining program to come forward and acknowledge his role.
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Colonel Shaffer said that his role in Able Danger was as the program's liaison with the Defense Intelligence Agency in Washington, and that he was not an intelligence analyst. The interview with Colonel Shaffer on Monday night was arranged for The New York Times and Fox News by Representative Curt Weldon, the Pennsylvania Republican who is vice chairman of the House Armed Services Committee and a champion of data-mining programs like Able Danger.