US President George W Bush has welcomed the report of the bipartisan commission set up to investigate the 11 September terror attacks.
Bush said he was ready to act where necessary
Mr Bush said he agreed with its conclusion that the hijackers had exploited deep institutional failings.
But he stopped short of endorsing a key proposal to establish a national intelligence director.
The commission recommends a wide-ranging overhaul of US intelligence services and congressional oversight.
"Where government needs to act, we will," President George W Bush said after receiving his copy of the report which follows two years of exhaustive investigation.
"We will give serious consideration to every idea because we share a common goal," he added.
His Democratic challenger in November's presidential elections, John Kerry, urged the president to act quickly.
"If I am elected president and there has still not been sufficient progress on these issues, I will not wait a single day more. I will lead," he said.
Observers say congressional action on the report is unlikely until after the election.
Congress goes into its summer recess soon. By the time it reconvenes in September, Washington will be in full electioneering mode.
Intelligence bodies have come under harsh criticism for failing to avert the airliner hijackings, in which nearly 3,000 people died.
But no single individual is to blame, said Republican chairman Thomas Kean of the panel that produced the report.
"Yet individuals and institutions cannot be absolved of responsibility," he said.
Bob Hughes, the father of a victim of the attacks, said: "There is plenty of blame to go around."
"There's really no closure for me and my wife," Mr Hughes said.
Among the report's recommendations are:
BBC News Online world affairs correspondent Paul Reynolds says the proposals amount to the most significant change since the CIA was founded after World War II.
- the creation of a national counter-terrorism centre "unifying strategic intelligence and operational planning against Islamist terrorists across the foreign-domestic divide"
- the establishment of a new national intelligence director to unify the intelligence community
- creating a "network-based information sharing system that transcends traditional governmental boundaries"
- strengthening congressional oversight
The National Commission on Terrorist Attacks Upon the United States published the final report - almost 600 pages long - following testimony from more than 1,000 witnesses and examination of as many classified documents.
"The most important failure was one of imagination. We do not believe leaders understood the gravity of the threat," said the 10-member panel.
The report said: "The 9/11 attacks were a shock, but they should not have come as a surprise.
"Islamist extremists had given plenty of warning that they meant to kill Americans indiscriminately and in large numbers."
But "terrorism was not the overriding national security concern for the US government under either the [former President Bill] Clinton or pre-9/11 Bush administration," it said.
"The United States government was simply not active enough in combating the terrorist threat before 9/11," Mr Kean said.
He added that it had been impossible to determine whether the 11 September attacks could have been prevented - it was "possible", but this could not be borne out by facts.
"An attack of even greater magnitude is now possible and even probable. We do not have the luxury of time. We must prepare and we must act," Mr Kean said.