WASHINGTON -- The U.S. government failed to prevent the worst assault on American soil because it never understood the "gravity" of the threat posed by al-Qaida operatives who exploited intelligence lapses on Sept. 11, 2001, the final 9/11 report concludes.

Final Report: 9/11 Public Discourse Project July 2004: 9/11 Commission Findings 9/11 Report: Joint Congressional Inquiry Members: 9/11 Panel Images: 9/11 Testimony Synopsis

"We were unprepared," commission chairman Thomas Kean said to open a 90-minute news conference to release the report. "We did not grasp the magnitude of a threat that had been gathering over a considerable period of time."

Full Text: 9/11 Commission's Final Report

The 567-page report by the federally appointed panel of five Democrats and five Republicans concludes that the "most important failure" before the attacks was "one of imagination." The statement did not blame a particular administration, specifically President George W. Bush or former President Bill Clinton.

"They understood the threat existed," said Lee Hamilton, commission vice chairman. "But they did not understand that 3,000 people could be killed in an hour's time. We simply did not put together the signals to understand that terrorism was the predominant national security threat to the United States."

Kean and Hamilton listed many missteps before Sept. 11, 2001, when nearly 3,000 Americans and U.S. visitors died in New York, Washington and Pennsylvania, and said they kept U.S. authorities behind the pace of "a very nimble enemy" -- who, Hamilton said, "knew they could get on a plane with a 4-inch knife but probably not a 6-inch knife."

"This was a failure of policy, management, capability -- and above all, a failure of imagination," Kean said. "We cannot know if any step or series of steps could have defeated (the 9/11 plot)."

He added that none of the antiterrorism measures taken before Sept. 11 "disturbed or delayed the progress of the al-Qaida plotters."

Kean -- whose panel has unveiled a series of recommendations, chiefly a Cabinet-level intelligence director -- also had an ominous warning.

"Every expert with whom we spoke told us that an attack of this or greater magnitude is possible -- even probable," Kean said. "We don't have the luxury of time."

The report says there should be a unified command for the more than a dozen federal agencies that now collect intelligence overseas and at home. Leading that center would be a new national intelligence director, confirmed by the Senate -- someone who would be just below full Cabinet rank, and would report directly to the president. The director would "influence the budget and leadership" of the CIA, FBI, Homeland Security Department and Pentagon.

Hamilton said the United States needs reform in the intelligence community and in Congress.

"We need unity of effort in the intelligence community," Hamilton said.

Panelists Address Iraq, Saudi Questions

Asked by a reporter about Iraq's possible link to the 9/11 attacks, Kean and Hamilton said the panel found no "concrete" link between Iraq and 9/11.

Kean said the panel knew of al-Qaida operatives holding meetings with representatives of Saddam Hussein's regime before the attacks.

"There was a relationship," Kean said. "But there was no collaborative relationship" with respect to 9/11.

Hamilton addressed questions of alleged Saudi government involvement in the 9/11 plot.

"We have found no evidence of the Saudi government involved in the plot," Hamilton said. "We have found evidence of individual Saudis -- whether wittingly or unwittingly -- whose funds found their way to terrorists."

Hamilton said improving U.S.-Saudi relations is important.

"They are helping us now on the terrorist-financing issue," Hamilton said. "This is a very difficult relationship for the United States and has been for a very long time. We want to see this relationship get more depth."

Hamilton also addressed a question about possible involvement by Iran or the Iran-based terrorist group Hezbollah.

"We considered these questions, and it is our view that al-Qaida planned these attack by themselves," Hamilton said.

Panel: Passengers Never Breached Flight 93 Cockpit

Passengers on United Airlines Flight 93, which crashed into a field in rural Pennsylvania on Sept. 11, fought valiantly but never breached the cockpit of the hijacked jet, according to the 9/11 report.

Some victims' families believed passengers fought hijackers inside the cockpit before the plane's rapid descent.

Gleaning its account from cockpit recorder and flight data, the commission concluded the hijacker-pilot rocked the plane's wings and ordered a henchman to block the door when passengers mounted an attack.

Seconds later, an unidentified passenger yelled, "In the cockpit! If we don't, we die!"

The hijacker-pilot said, "Allah is the greatest!" He asked a fellow hijacker whether to "put it down."

The man replied, "Yes. Put it in, and pull it down."

About 90 seconds later, the plane tore into a field at more than 580 miles per hour. Everyone aboard died.

The report praises passengers' courage and says their fight "saved the lives of countless others."

Kean: No Comparison To Pearl Harbor

Kean said some Americans have likened the tragedy of the 9/11 attacks to Pearl Harbor and the assassination of former President John F. Kennedy.

"There is no comparison," Kean said. "This was a moment that was unique in its horror in our history."

Bush Vows Action When Needed

Bush, who was briefed on the report Thursday morning before the document was released in full, said he told the leaders of the commission that "where the government needs to act, we will."

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Bush Embraces 9/11 Report

Bush said the commission is putting forward a "common sense approach" on how to move forward in the fight against terrorism. He said they're making "very constructive recommendations."

The report is sharply critical of the nation's intelligence gathering, concluding that the hijackers exploited "deep institutional failings" within the government. The report also lists numerous missed opportunities to stop the hijackers.

In presenting Bush with the report, Kean thanked the president for his administration's cooperation in the investigation.

Bush said the panel recognized what he and the nation also recognize -- that terrorism is still a threat. He said the government has an obligation to do everything in its power to protect the American people.

Panelist John Lehman, addressing questions of no blame for either Bush or Clinton, said Wednesday that the report doesn't place direct blame on a particular administration and "editorialize" because the intelligence system has been broken for a long time.

One official said the report concludes that Bush and Clinton took the threat posed by al-Qaida seriously and were "genuinely concerned."

Report Rips Intelligence Gathering

The report's toughest criticism is aimed at the FBI and the CIA. The commission said poor information sharing and intelligence analysis were key failures that contributed to the plot.

But the panel decided against creating a domestic spying agency like Britain's MI5. It apparently decided that FBI Director Robert Mueller's reform efforts are on the right track.

One official said the commission did find that the FBI was not set up to collect intelligence domestically -- in part because of civil liberties concerns.

Loved Ones Of Victims React

A woman whose husband died at the Pentagon on Sept. 11 said she's "very impressed" with the commission's final report.

Christine Fisher said the commissioners were sincere, honest and thorough.

Bob Hughes, whose son Chris was killed in the attack on the World Trade Center, said he was particularly pleased that the commissioners' conclusions were unanimous.

Hughes also agreed with the commissioners that there should have been better communication between the intelligence agencies. He said the changes they suggested should be implemented for the good of the United States.

But a man whose brother was killed when a jetliner hit the Pentagon doubted whether the changes will be put into place quickly. Brad Burlingame said he's already hearing there isn't time to take significant action until after the November election.

"Frankly, that's unsatisfactory," Burlingame said.

Pearl Williams, who lost a son in the Pentagon attack, said her son would want her to look at the lessons learned from the attack -- and move forward.