By RUPERT CORNWELL in Washington
National security adviser Condoleezza Rice today admitted that the Bush administration was not on a "war footing" before the terrorist attacks of September 11 2001.
But she said there was no "silver bullet" that could have prevented the attacks - and that any hopes of doing so were thwarted by an endemic lack of communication between the CIA and the FBI.
In more than two and a half hours of avidly awaited testimony to the commission examining the background of 9/11, Ms Rice delivered a composed, articulate and forceful defence of Mr Bush, insisting he was fully aware of the threat posed by al Qaeda.
But, however alarming, none of the intense terrorist 'chatter' picked up in the summer of 2001 gave specific indications - in her words - of "when, where and how" the feared strike might be carried out.
Instead, she singled out the "structural and legal impediments" in the collection and pooling of information by the FBI, responsible for domestic law enforcement, and the CIA which handled foreign intelligence.
Thus suspicions by FBI field offices in 2001 about Middle Eastern men attending flight schools in Arizona and Minnesota were not properly circulated. Nor was the CIA's awareness that two of the future hijackers, known al Qaeda operatives, were already in the US.
Mr Bush had long refused to allow his closest foreign policy adviser to give public evidence under oath to the commission, before yielding to overwhelming pressure for Ms Rice to do so.
According to White House officials, the President (who alongside vice-President Dick Cheney will meet privately with the commission later this month) watched her performance at his Texas ranch, where he is spending Easter week.
He will probably have been well satisfied -- though in the current fiercely partisan election-year climate, Ms Rice is unlikely to have changed many minds.
Republicans on the committee were generally polite. But Democrats maintained she had not dispelled doubts that Mr Bush might have done more to prevent 9/11.
The toughest questioning came from two Democrats, the former Nebraska senator Bob Kerrey and Richard Ben Veniste, prosecutor for the Watergate committee which pursued Richard Nixon in the early 1970s.
Taking issue with her chief critic, she insisted that former White House counter-terrorism chief Richard Clarke had never asked for a specific meeting with Mr Bush to underline the grave threat posed by al Qaeda.
She also denied his claim that the Bush administration had not "shaken the tree" with sufficient vigour, to dislodge precious pieces of information from the federal bureaucracy that might have pointed to the impending attack. The fault, she said, was in the system, not at the White House.
Much of the criticism levelled at Mr Bush surrounds the 'PDB' or Presidential Daily Briefing provided by the CIA on August 6 2001, which is said to have warned that terrorists might use hijacked aircraft to attack the US.
But Ms Rice claimed that brief was in response to a request by Mr Bush for an update on the terrorist menace to the US. It recapped existing material, but did not specifically warn of an impending attack.
Democrats last night renewed demands for total declassification of that particular PDB.
She maintained - as did top Clinton administration officials in separate testimony to the commission last month - that before 9/11 no-one was recommending a full-scale invasion of Afghanistan.
However Bush, she said, had already decided that a strategic offensive against terrorism was needed, to replace the Clinton-era approach of "swatting flies" with small-scale retaliatory strikes against al Qaeda.
But Mr Kerrey pointed to the Bush team's failure to respond to the October 2000 attack on the USS Cole, even when the FBI had established that Osama bin Laden's organisation was responsible.
Angrily he asked Ms Rice: "What fly did the President swat? Name me one swatted fly?"
Now everything is different, argued Ms Rice. Terrorism could only be tackled with a pre-emptive action.
"We have to be right 100 per cent of the time, the terrorists only need to be successful once," she said.
"If we learnt anything on 9/11 it was that we must strike first....We could seek a narrow victory, or go for broader goals. President Bush chose the latter course."
As a result, brutal regimes had been removed in Afghanistan and Iraq, while Libya had agreed to give up its weapons of mass destruction programmes.
Statement to the 9-11 Panel:
Dr. Condoleezza Rice, Assistant to the President for National Security Affairs