The US Congressional report cites lapses among the Federal Bureau of Investigations (FBI) and the Central Intelligence Agency (CIA), along with other US government bodies.
Some senators are now calling for the resignation of CIA head George Tenet, although most of the blame is directed at the FBI.
The two agencies did not share information that might have helped alert them to the 9/11 attack which shook the world.
The 900-page report, which indicates the attacks could have been prevented, lays blame on a breakdown in communication and co-operation between intelligence agencies.
“The report points out to a lack of co-operation among US intelligence services,” Senator Richard Shelby told a US television.
The document reports that high-ranking officials at the White House had been informed during the summer of 2001 of possible plans by al-Qaeda, blamed for the incidents, to hijack commercial planes and launch attacks, according to Congressional sources.
The congressional commission report presents a chronology of ignored warnings and other signs not shared by the FBI and CIA in the run up to the attacks against the World Trade Centre in New York City and the Pentagon building in Washington.
Some Congress members believe
Saudi Arabia played a role
Florida Senator Bob Graham said the document indicates there needs to be a change in collecting intelligence.
“It’s increasingly going to be the old-fashioned spies, a human being who can get inside those organisations, find out what their plans are and be able to then attack them militarily,” said Graham, who formerly chaired the Senate Intelligence Committee.
The report raises questions over the alleged role played by Saudi Arabia in the run up to the events. But they remained unanswered since the White House refuses to declassify 28 pages of the report.
The move drew criticism from some Congress members, who called on the White House to allow information to be made public.
US Senator Chuck Schumer accused the White House of “coddling and cover-up when it comes to the Saudis”.
“The (Bush) administration’s whole policy toward Saudi Arabia is backward and needs to make a 180 degree turn immediately,” said Schumer.