The Sept. 11 commission (search) will release its 500-plus-page report Thursday detailing significant intelligence lapses surrounding the deadly attacks on the United States, but it won't say the events that left about 3,000 people dead could have been prevented.

President Bush said Wednesday his administration is doing everything possible to prevent another terrorist attack as he braced for the report.

"I look forward to receiving the report," Bush said in the Rose Garden as he signed a bill at the White House to develop and stockpile vaccines and other antidotes to biological and chemical weapons.

"I will continue to work with the Congress and state and local governments to build on the homeland security improvements we have already made," Bush continued. "Every American can be certain that their government will continue doing everything in our power to prevent a terrorist attack, and if the terrorists do strike we will be better prepared to defend our people because of the good law I sign today."

Commission Chairman Thomas Kean (search), a former New Jersey governor, and Democratic Vice Chairman Lee Hamilton, a former Indiana congressman, were briefing Bush's national security adviser, Condoleezza Rice, and White House counsel Alberto Gonzalez Wednesday on the panel's findings.

The report will be "a measure about whether we have taken changes in the meantime [since Sept. 11, 2001] to make sure it can't happen again and to make sure these agencies are cooperating … whether we've taken enough action has yet to be analyzed," Sen. Charles Grassley, R-Iowa, told FOX News on Wednesday, noting that the FBI and CIA are already talking more now than they were on Sept. 10, 2001. "This is a measuring step as we move forward."

Sen. John Corzine, D-N.J., told FOX News that the focus of the report will be on how to prevent another Sept. 11 and "for those who want to turn it into a program of political argument in a political season — I think they're doing a disservice to the people who lost their lives on 9/11. This is about what went wrong and how we can take steps to prevent it."

On whether the report will produce any real bureaucratic reform, Corzine said: "I think it's one piece of examination of our intelligence structure and how intelligence is used in terms of making policy."

"This isn't about Republicans or Democrats," Corzine continued. "This is about making sure our national security and homeland security are absolutely in top shape as we go forward."

The report includes a list of 10 "operational opportunities" that the government missed to potentially unravel the Sept. 11 plot, a government official who read the document told The Washington Post. Six of the incidents listed came during the Bush administration and four were during the Clinton years, that official said.

Another government official who has been briefed on the report told the Post that the tally of missed opportunities includes the CIA's failure to add two hijackers' names to a terrorism watch list; the FBI's handling of the August 2001 arrest of Zacarias Moussaoui (search), who has been accused of conspiring in the Sept. 11 plot; and several failed attempts to kill or capture Usama bin Laden.

The report also notes, however, the inherent difficulties that intelligence agencies have in assembling a clear picture of a terrorist threat, one official said.

"The president would have moved heaven and earth to stop those attacks," White House spokesman Scott McClellan said Wednesday. "He's made that very clear. The fact of the matter is: We were not on war footing prior to Sept. 11. Now we are a nation at war. We are engaged in a global war on terrorism. But the threat from terrorism was building for more than a decade."

New Intel Chief Proposed

The panel of five Republicans and five Democrats also will call for a controversial new Cabinet-level intelligence chief and recommend combining the House and Senate intelligence committees and removing term limits from committee members, according to GOP House leaders who were informally briefed on the report Tuesday.

"It is time to put somebody in charge of the entire intelligence community, and give that person the budgetary and statutory authority to accomplish the job," said Sen. Dianne Feinstein, D-Calif., who has introduced a bill to create the position and has bipartisan support from five colleagues.

Sen. Arlen Specter, R-Penn., told FOX News that such a post has been necessary for some time.

Of the CIA and FBI, he said, "the fact is, both of those agencies have cultures of concealment — they just don't share information."

Some Republicans and Democrats are worried that a national intelligence czar position would become too political by giving the normally apolitical intelligence chief a seat at the president's policy-making table.

Intelligence agencies will "fight it fiercely," Specter said of the intelligence czar position, and there's already opposition to such an idea on Capitol Hill because some committees may have to give up

"It's time we stopped worrying about power and started to worry about the security of the American people," Specter said.

But Congress isn't likely to undertake major revisions of the nation's intelligence operations this year, House Speaker Dennis Hastert said, casting doubt on the commission's push for immediate changes once its final report is released.

Hastert, R-Ill., said any legislative action on the panel's recommendations probably won't occur until after the next president is inaugurated in January, given the limited time Congress has remaining this year.

"It's a very difficult time to squeeze out and have the oversight and the testimony to put new legislation in place," Hastert said.

House Majority Whip Roy Blunt, R-Mo., called the proposal to remove term limits a "particularly bad idea," saying committee members would become overly ingrained within the intelligence community. Currently, limits are set at eight years for senators and six years for House members, with some exceptions.

Commissioners plan an aggressive lobbying effort in the summer and fall to push recommended changes. The panel will split into bipartisan pairs and travel nationwide for speaking engagements and media appearances.

"Commissioners have all said they hoped the report would not just go on a shelf as so many others have," commission spokesman Al Felzenberg said. "They said they hoped both presidential campaigns would endorse the recommendations and Congress would act."

'Broken' Intelligence System

The harshest criticism will be leveled at the FBI and CIA, with the panel citing poor information-sharing and intelligence analysis as key factors that allowed the hijackers to carry out their plot.

In the end, the commission did not want to draw a conclusion on that major point, believing it could open the way to partisan sniping in a presidential election year. Both Kean and Hamilton have said the attacks conceivably could have been prevented.

"My personal view is that the intelligence system we have has been broken for a long time," said Republican commissioner John Lehman, a former Navy secretary. "But we wanted to let the American people make up their mind. They don't need our editorializing."

Commissioners have said it is important for them to endorse the report unanimously so their findings and recommendations are not seen as partisan. A poll released Wednesday by the Pew Research Center for the People & the Press found 61 percent of Americans believe the commission has done a good job. The support was nearly even among Republicans and Democrats.

Advisers to Democratic presidential candidate John Kerry have said they hope to use the report to show that in the summer of 2001, the Bush administration was inattentive to threats of a possible attack.

The Clinton administration, meanwhile, is under fresh scrutiny after federal authorities said they were investigating former national security adviser Sandy Berger (search) in connection with the disappearance of highly classified terrorism documents.

Felzenberg, the commission spokesman, said the Berger probe wouldn't affect the panel's final report.

FOX News' Liza Porteus and The Associated Press contributed to this report.