WASHINGTON (AP) - Prior to the Sept. 11, 2001, terrorist attacks, the CIA failed to act on intelligence it had about hijackers, the FBI was unable to track al-Qaida in the United States, and key National Security Agency communications intercepts never were circulated, a congressional investigation has concluded.

But even had these and many other failures not occurred, no evidence surfaced in the probe by the House and Senate intelligence committees to show that the government could have prevented the attacks that killed more than 3,000 people in New York, Washington and Pennsylvania.

A 900-page declassified version of the report being released Thursday was expected to provide fresh details of the Sept. 11 plot and government failures but no ''smoking guns.'' Excerpts of the report were provided to The Associated Press before its official release.

''Anybody who makes an assertion that this could have been prevented is making a political statement because there is no evidence, no information that was shared with the top people in our government that could have led them to believe this was going to happen,'' said Rep. Ray LaHood, R-Ill., a House intelligence committee member. ''It wasn't there.''

Yet the report makes clear there were ample warning signs that Osama bin Laden was planning attacks within the United States, and several opportunities to learn about the plot were missed by intelligence and law enforcement agencies.

For instance, the NSA, the nation's key signals intelligence agency, intercepted conversations by early 1999 indicating that two future hijackers were connected to a suspected al-Qaida facility in the Middle East, but that information was not passed on to other agencies.