Members of the independent commission that investigated the Sept. 11 terror attacks called on Congress to determine whether the Pentagon withheld intelligence information showing that a secret American military unit had identified Mohammed Atta and three other hijackers as potential threats more than a year before the attacks.

The former commission members said the information, if true, could rewrite an important chapter of the history of the intelligence failures before Sept. 11, 2001.

"I think this is a big deal," said John F. Lehman, a Republican member of the commission who was Navy secretary in the Reagan administration. "The issue is whether there was in fact surveillance before 9/11 of Atta and, if so, why weren't we told about it? Who made the decision not to brief the commission's staff or the commissioners?"

Mr. Lehman and other commissioners said that because the panel had been formally disbanded for a year, the investigation would need to be taken up by Congress, possibly by the House and Senate Intelligence Committees.

"If this is true, somebody should be looking into it," said Thomas H. Kean, the commission chairman and a former Republican governor of New Jersey.

Detailed accounts about the findings of the secret operation, known as Able Danger, were offered this week by Representative Curt Weldon, the Pennsylvania Republican who is vice chairman of the House Armed Services Committee, and by a former defense intelligence official.