DAVID JOHNSTON and DOUGLAS JEHL, The New York Times, report:

WASHINGTON, July 22 - The Clinton and Bush administrations failed to grasp the gravity of the threat from Al Qaeda before the Sept. 11, 2001, attacks and left counterterrorism efforts to a disparate collection of uncoordinated, underfinanced and dysfunctional government agencies, the commission on the attacks said in its final report published on Thursday.

“Across the government, there were failures of imagination, policy, capabilities and management,” the panel said in its report, which was harshly critical of how the intelligence, law enforcement and military branches performed before the attacks.

In a series of findings that were searing in tone, sweeping in judgment and backed by voluminous reporting, the report said senior officials were repeatedly warned about Osama bin Laden’s intentions, but failed to respond with an aggressive sense of national purpose.

“Terrorism was not the overriding national security concern for the U.S. government under either the Clinton or the pre 9/11 Bush administration,” the report said.

In contrast to most government reports, the findings were presented in a dramatic, often gripping narrative style with chapter headings like “We Have Some Planes” and the “The System Was Blinking Red.”

In a tone that sometimes resembled a paperback thriller, the report chronicled Mr. bin Laden’s rise as a global terrorist leader and the agonizingly slow recognition by the Clinton and Bush administrations of the danger that his network represented.

The account described in authoritative detail how the plot, despite setbacks, gathered shape and direction and how it finally struck with four nearly simultaneous hijackings even as the national security experts here continued to ponder a counterterrorism strategy and the agencies responsible for protecting the country were completely blindsided.

Many findings were foreshadowed in the 17 staff reports previously made public, but the new report had new information about the Sept. 11 attacks, including a detailed account of how passengers on Flight 93 tried to gain control of their hijacked plane.

The report did not address directly whether the attacks might have been prevented.

“Since the plotters were flexible and resourceful, we cannot know whether any single step or series of steps would have defeated them,” the commissioners wrote in the executive summary. “What we can say with confidence is that none of the measures adopted by the U.S. government, from 1998 to 2001, disturbed or even delayed the progress of the Al Qaeda plot.”

Senior officials in both administrations, the report said, regarded an invasion of Afghanistan before Sept. 11 as “practically inconceivable.” The ambivalent attitude continued up to the attacks. In one internal memorandum on Sept. 4, 2001, Richard A. Clarke, who was the White House counterterrorism adviser, sought to protest what he regarded as foot dragging in the Pentagon and C.I.A.

“Are we serious about dealing with the al Qida threat?” Mr. Clarke asked. “Is al Qida a big deal?”

In the end, the commissioners reached no definitive verdict on whether Mr. Clinton or Mr. Bush deserved greater blame for the lapses and inaction. The report seemed to portray Mr. Clinton as better informed and more intensely engaged than Mr. Bush. In contrast to Mr. Bush, the report said, Mr. Clinton and his national security adviser, Samuel R. Berger, had “a special daily pipeline of reports feeding them the latest updates on bin Laden’s reported location.”

But neither administration received much praise. According to the report, Mr. Clinton, Mr. Bush and their advisers said in interviews with the panel that “they understood bin Laden was a danger.'’

“But given the character and pace of their policy efforts,'’ the study said, “we do not believe they understood just how many Al Qaeda might kill and how soon it might do it.”

Different sections give contrasting accounts of responses by national security advisers under Mr. Clinton and Mr. Bush. It describes how Mr. Berger, under Mr. Clinton, took the lead in December 1999 in mobilizing the F.B.I. and other domestic agencies to address the so-called millennium plot, in which attacks planned in Jordan and Los Angeles were disrupted. By contrast, the report describes Condoleezza Rice and her deputy, Stephen Hadley, as not having regarded the coordination of domestic agencies as part of their responsibility after they took office in 2001, even as warnings of a possible attack continued to grow.

The report said of the Bush White House before Sept. 11: “The domestic agencies never mobilized in response to the threat. They did not have direction, and did not have a plan to institute.”

The report found no evidence that Iraq, Iran or Saudi Arabia provided operational or financial support to Al Qaeda as part of the Sept. 11 attacks. In contrast to the Bush administration, the panel singled out as most worthy of further investigation not Al Qaeda’s pre-Sept. 11 ties to Iraq, but its links to Iran.

The lapses, mistakes and bureaucratic inefficiencies that hobbled the government were apparent in every agency investigated, although the report did not fault any individuals for specific mistakes. The military had no plans to defeat Al Qaeda or kill or capture Mr. bin Laden or his chief lieutenants. Diplomatic efforts failed to dislodge Mr. bin Laden from Afghanistan. Border authorities failed to detect false passports or recognize passports that had been fraudulently manipulated. Aviation security officials failed to expand lists of people to be excluded from flying or impose thorough passenger screening.

The C.I.A., responding to rapidly expanding priorities, and the F.B.I., bogged down by its case-oriented reactive approach, failed to share crucial information with each other and in some instances failed to follow up potentially important leads.

Immigration and aviation agencies were largely left outside the efforts. The emergency response by federal, state and local authorities on Sept. 11 was often “improvised and ineffective,” the report said, “even as extraordinary acts of heroism saved countless lives.”

“Our failures took place over many years and many administrations,” the panel chairman, Thomas H. Kean, said at a news conference. “There’s no single individual who is responsible for our failures. Yet individuals and institutions cannot be absolved of responsibility. Any person in a senior position within our government during this time bears some element of responsibility for our government’s actions.”

Specifically, in the years before the attacks, the report found, the intelligence agencies tried to combat the problems posed by Al Qaeda with tools and tactics that were inadequate and misdirected, principally those developed against the Soviet Union late in the cold war.

The report singled out the Central Intelligence Agency for serving at the forefront of counterterrorism, saying no agency did more to attack Al Qaeda before Sept. 11. But the report also described its response and those of other intelligence agencies as insufficient and hamstrung by a lack of resources, competing priorities and internal rivalries.

At no point after 1995, the report noted, did the intelligence agencies produce a new formal National Intelligence Estimate to sum up in a fully developed assessment the Qaeda threat. Even in summer 2001, it said, counterterrorism analysts were slow to perceive a broader threat. Before Sept. 11, the report said, the Clinton and Bush administrations limited the C.I.A. primarily to disrupt terrorism abroad and efforts via proxies. The operations tried to capture Mr. bin Laden and his aides in Afghanistan rather than kill him. Officials of the Counterterrorist Center at the intelligence agency and the National Security Council staff, the report notes, grew more frustrated.

At a briefing for reporters on Wednesday, senior C.I.A. officials acknowledged that its performance before Sept. 11 had flaws. But they also said the panel had underestimated the degree to which the agency had warned senior policy makers and shared information with other agencies about the terrorist threat.