The final report by the commission investigating the Sept. 11, 2001, attacks details as many as 10 missed opportunities by the Bush and Clinton administrations to detect or derail the deadly terrorist hijackings, but the panel stops short of saying the attacks should have been prevented, according to government officials and others familiar with the document.

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

But the nearly 600-page report acknowledges that many of the opportunities were long shots and that others would have required a lucky sequence of events to alter the outcome, said sources who declined to be identified because the commission wants the document kept secret until its release.

Another government official who has been briefed on the report said 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, who has been accused of conspiring in the plot; and several failed attempts to kill or capture Osama 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 list of missed opportunities is the latest revelation to emerge in recent days about the final report of the panel, known formally as the National Commission on Terrorist Attacks Upon the United States. The report details broad government failures in connection with the Sept. 11 plot and recommends a wide-ranging restructuring that would include a Cabinet-level intelligence director to oversee the CIA, the FBI and other intelligence agencies.

The report also concludes that al Qaeda's relationship with Iran and its client, the Hezbollah militant group, was far deeper and more long-standing than its links with Iraq, which never established operational ties with the terrorist group, said officials familiar with the document.

Among the newest findings is evidence, disclosed in media reports this week, that as many as 10 of the Sept. 11 hijackers transited through Iran before the hijackings.

The findings will again put the panel in the middle of a political battle over claims by President Bush, Vice President Cheney and other administration officials that Saddam Hussein and al Qaeda may have had significant ties. Bush said on Monday that U.S. officials were now probing possible Iranian links to the Sept. 11 attacks.

Commission and government officials stress there is no evidence indicating that Tehran knowingly aided in the Sept. 11 plot. But Iran's apparent willingness to allow al Qaeda members to roam across its borders underscores the complicated relationship that emerged between them despite historic animosity between Sunni and Shiite Muslims. There is compelling evidence that Shiite Iran continued to give al Qaeda leaders haven even after the Sept. 11 attacks, according to the commission report and other intelligence sources.

Yesterday, the commission's chairman, Thomas H. Kean (R), and vice chairman, Lee H. Hamilton (D), briefed House GOP leaders on the report. Democratic leaders are to be briefed today.

Over 20 months, the 10-member bipartisan commission has tread carefully on the overarching question of whether the attacks could have been, or should have been, prevented. Kean and Hamilton have said at various times that the attacks could conceivably have been thwarted, but they have stopped short of saying prevention was likely or reasonable.

The panel decided several months ago that it would not include such a definitive judgment in its final report, said one commission member interviewed this week. Rather, this commissioner said, the decision was made to outline missed opportunities while acknowledging the tenacity and adaptability of al Qaeda in reaching its goal.

"There clearly were many opportunities out there that were not taken advantage of," said the commissioner, who declined to talk publicly because of the embargo on releasing the report. "From that, some will conclude it could have been prevented, others will say it might have been prevented and the rest will say it's impossible to tell. . . . We said we couldn't get an answer to this."

Yet by detailing a list of missed opportunities, the Sept. 11 commission intends to send the message that different actions by government officials in the years leading up to the attacks could have had a profound impact on the plot's outcome, officials who have seen the report said.

In a series of interim staff reports issued this year, along with questioning of witnesses in public hearings, the commission has focused intensely on the Bush administration's actions in the summer of 2001 amid a heightened state of alert about an impending al Qaeda attack. Former counterterrorism coordinator Richard A. Clarke testified that the Bush administration was distracted in its first eight months and was less aggressive than the Clinton administration in addressing terrorism.

Two officials familiar with the report said several of the missed opportunities identified by the commission occurred during this time. After arresting Moussaoui, for example, the FBI failed to get a warrant to search his belongings and the bureau's acting director was not briefed on the case, although CIA Director George J. Tenet was, according to commission testimony.

The commission's report will also examine at length a series of missteps and lapses that began with the CIA's failure to adequately follow up on a meeting of al Qaeda associates in Malaysia in January 2000 attended by two future hijackers, Nawaf Alhazmi and Khalid Almihdhar.

The CIA neglected to add their names to a terrorist watch list to prevent them from entering the United States, and the FBI was slow and meek in its response once notified, according to previous findings and testimony.

Staff writer Walter Pincus contributed to this report.

House Republicans, from left, Christopher Cox (Calif.), Majority Leader Tom DeLay (Tex.), Speaker J. Dennis Hastert (Ill.), F. James Sensenbrenner Jr. (Wis.) and Majority Whip Roy Blunt (Mo.) were briefed yesterday by the commission. The panel's book-length report is to be released tomorrow.