The Sept. 11 commission will investigate a claim that U.S. defense intelligence officials identified ringleader Mohamed Atta and three other hijackers as a likely part of an al Qaeda cell more than a year before the 2001 hijackings but did not forward the information to law enforcement.

Rep. Curt Weldon (R-Pa.), vice chairman of the House Armed Services and Homeland Security committees, said yesterday that the men were identified in 1999 by a classified military intelligence unit known as "Able Danger." If true, that is an earlier link to al Qaeda than any previously disclosed intelligence about Atta.

Lee H. Hamilton, co-chairman of the Sept. 11 commission, said the information warrants a review. He said he hoped the panel could issue a statement on its findings by the end of the week.

"The 9/11 commission did not learn of any U.S. government knowledge prior to 9/11 of surveillance of Mohamed Atta or of his cell," Hamilton said.

The commission's final report, issued last year, recounted numerous government mistakes that allowed the hijackers to succeed in their attacks on the World Trade Center and the Pentagon. Among them was a failure to share intelligence within and among agencies.