The memos were revised and renewed thereafter every 45 days. The report said that the president consistently gave that authorization for the surveillance activity, and that both CIA chief Tenet and his successor, Porter Goss, never withheld their signatures from threat assessment memoranda.

The report also questions the legal advice used by President Bush to set up the program, pinpointing omissions and questionable legal memos written by Yoo at the Justice Department.

The report suggests Yoo ignored an explicit provision in the FISA law designed to restrict the government's authority to conduct electronic surveillance during wartime. And it said flaws in Yoo's memos later presented "a serious impediment" to recertifying the program.

Congress required the review of the so-called warrantless wiretapping program last year when it revised the Foreign Intelligence Surveillance Act. FISA is a 30 year-old law that created a secret court to oversee government electronic surveillance.

The inspectors general of the CIA, Justice Department, Defense Department, National Security Agency and Office of the National Intelligence Director also reviewed the Bush-era surveillance program.