The Sept. 11 commission (search) has long been vocal about the government's mishandling of terror-related intelligence prior to the attacks, but its final report will contain several significant revelations.

The 575-page report that will be released on Thursday addresses speculation that Saudi nationals with ties to the Bush administration were permitted to fly out of the United States after the attacks while all other planes were grounded. One official familiar with the report told FOX News the commission independently confirmed that no planes lifted off while the flight ban was in effect, and that no one thought to have any ties to the attacks was permitted to leave the United States.

The Bush administration has long held that certain members of Usama bin Laden's (search) family known to have no current relations with the Al Qaeda leader or any terror-related activity were permitted to leave the United States after the flight ban for their own safety.

The report will also further explore the relationship between Al Qaeda (search) and Saddam Hussein's regime in Iraq.

While there was no "collaborative operational relationship for carrying out attacks against the United States," the commissioners found that Saddam Hussein tolerated and may have helped Qaeda-linked groups such as Ansar al Islam (search) in northern Iraq, officials who have seen the report told FOX News.

Moreover, the commissioners found that bin Laden sought cooperation from Iraq on more occasions than were previously known. In March of 1998, two Al Qaeda leaders met with Iraqi intelligence agents in Baghdad. Four months later, Iraqi officials met with Taliban and Al Qaeda leaders – possibly bin Laden himself – in Afghanistan.

'Deep Institutional Failures'

The Sept. 11 commission found that both Presidents Clinton and Bush took the Al Qaeda threat seriously, and neither could be blamed with failing to prevent the attacks.

"Both presidents were genuinely concerned by the danger posed by Al Qaeda," an official familiar with the report told FOX News.

In addition, the now-infamous Aug. 6, 2001, presidential daily briefing titled "Bin Laden Determined to Strike in U.S." was the first and only report referencing a domestic terror threat given to President Bush, and was a response to the president's own inquiries.

The report finds that Clinton and Bush administration officials were on alert for imminent threats from Al Qaeda, but that "deep institutional failures in our government going back many years" may have been partly to blame for the Unites States' lack of preparedness for the attacks.

The hijackers tested, determined and took advantage of those holes in the nation's terror-prevention system, according to the report. Surveillance video showed that four of the five hijackers set off metal detectors at Dulles International Airport on the morning of Sept. 11, 2001, and managed to board American Airlines Flight 77 anyway.

An airport screener can be seen hand-checking the baggage of one hijacker in the video that was released on Wednesday. Another hijacker was seen being manually checked with a handheld metal detector by a screener after he set off a second alarm.

It is believed the hijackers were carrying on their person or in their baggage knives which they later used to hijack the flight, which crashed into the Pentagon at 9:39 a.m. on Sept. 11, 2001.

The report concludes that the systematic lapses that allowed the hijackers to plot the attacks without setting off alarms on the national level are ongoing, and that the United States, while safer, is still not safe.

Drawing Lessons From the Attacks

The Sept. 11 commission spent 20 months investigating how the hijackers were able to mount the worst terrorist attack in U.S. history, killing nearly 3,000 people and demolishing the World Trade Center's twin towers. The 575-page report, culled from 2.5 million documents and 900 interviews with past and present government officials, is a "fascinating" documentation, one official told FOX News.

White House officials and congressional leaders were briefed Wednesday on the panel's findings, and Bush is to receive a copy of the report Thursday, just before it is released to the public.

Bush, bracing for a report that will be sharply critical of the government's intelligence-gathering, said he looked forward to reading the report and the administration is doing everything possible to prevent another terrorist attack.

"Had we had any inkling whatsoever that terrorists were about to attack our country, we would have moved heaven and earth to protect America," he said. "I'm confident President Clinton would have done the same thing. Any president would."

While administration officials offered a preview of the report, their summary was far from a complete accounting of the commission's findings.

Less than four months before the presidential election, the commission's work already has ignited partisan debate over whether Bush took sufficient steps to deal with terrorism in the first year of his administration.

As expected, the report will call for creating a Cabinet-level national director of intelligence with authority over the CIA, FBI and other agencies. The White House administration is reserving judgment on that recommendation, and officials doubt it could be approved by Congress this year.

Four administration officials briefed reporters on the content of the report on condition of anonymity because it has not been publicly released.

"Rather than finding that there was a failure at the presidential level, what they find though is that there are failings and that there were deep institutional failings within our government," an official said. "And that's what they really examine at some length over a long period of time — that there were a variety of factors spanning many years and many administrations that contributed to a failure to share information amongst agencies for both legal and policy reasons."

In particular, the official said, the commission found the FBI was not set up to collect intelligence domestically, in part because of civil liberties concerns.

The report also concludes there was a "failure of imagination" to provide either Bush or Clinton with new options — particularly military options — to deal with Al Qaeda, the official said. There was a failure to adapt to the post-Cold War era, and people just kept trying the same kinds of things that didn't work, the official said.

The report lists a series of missed operational opportunities to stop the hijackers, such as the bungled attempts to kill or capture bin Laden and the FBI's handling of Zacarias Moussaoui, who was arrested in August 2001 before the hijackings and has been accused of conspiring in the plot, the official said.

Commissioners have said the report also will fault Congress for poor oversight of intelligence gathering and criticize government agencies for their emergency responses to the attacks.

The harshest criticism will be leveled at the FBI and CIA, with the panel citing poor information sharing and intelligence analysis as key failures that contributed to the plot.

But the 10-member panel declined to recommend a separate domestic spy agency modeled after Britain's MI5, deciding that reform efforts by FBI Director Robert Mueller were on the right track despite the FBI's historical focus on law enforcement, said Rep. Jim Turner, D-Texas.

"What they've concluded is, the FBI is moving in the right direction — it has some capabilities in place, others are developing — and my sense is they chose not to disrupt that process," said Turner, the top Democrat on the House Homeland Security Committee.

The commission's proposals are a victory for Mueller, who sought to respond to withering criticism of the FBI after Sept. 11 by making counterterrorism the agency's primary mission. Mueller has repeatedly argued that a new domestic intelligence service would be duplicative and raise civil liberties concerns.

In June, Mueller told Congress he was working to create an intelligence service largely independent from the rest of the FBI, with its own budget and with a chief reporting to Mueller.

"Intelligence functions are woven throughout the fabric of the bureau, and any changes to this integrated approach would be counterproductive," Mueller told House lawmakers last month.

FOX News' Jim Angle, Bret Baier, Jane Roh and The Associated Press contributed to this report.