WASHINGTON, Dec. 10  Lawyers within the clandestine branch of the Central Intelligence Agency gave written approval in advance to the destruction in 2005 of hundreds of hours of videotapes documenting interrogations of two lieutenants from Al Qaeda, according to a former senior intelligence official with direct knowledge of the episode.

The involvement of agency lawyers in the decision making would widen the scope of the inquiries into the matter that have now begun in Congress and within the Justice Department. Any written documents are certain to be a focus of government investigators as they try to reconstruct the events leading up to the tapes’ destruction.

The former intelligence official acknowledged that there had been nearly two years of debate among government agencies about what to do with the tapes, and that lawyers within the White House and the Justice Department had in 2003 advised against a plan to destroy them. But the official said that C.I.A. officials had continued to press the White House for a firm decision, and that the C.I.A. was never given a direct order not to destroy the tapes.

“They never told us, ‘Hell, no,’” he said. “If somebody had said, ‘You cannot destroy them,’ we would not have destroyed them.”