A prominent member of the official commission looking into the attacks said they could have been prevented had US law enforcement and intelligence officials followed up on leads pointing to suspected "terrorists" at work in the United States.
But Bush said there was no way the administration could have prevented the hijacked airliners slamming into the World Trade Centre towers in New York and the Defence Department headquarters in Washington.
"I can't say it as plainly as this: Had I known, we would have acted," Bush insisted on Sunday to reporters on a visit to Ford Hood military base in Texas.
"I am satisfied that I never saw any intelligence that indicated there was going to be an attack on America: a time, and a place of an attack," he added while conceding "of course we knew that America was hated by Usama bin Ladin."
The White House on Saturday released a Presidential daily briefing sent to Bush on 6 August 2001, which warned that al-Qaida had penetrated the US and of possible plane hijackings.
Bob Kerrey, a former senator and leading Democratic member of the September 11 commission, wrote in a New York Times commentary on Sunday that the attacks could have been avoided.
"I can't say it as plainly as this: Had I known, we would have acted"
But former FBI director Louis Freeh said the country was not ready for an all-out "counterterrorism" campaign before the attacks on New York and Washington.
"The fact that terrorism and the war being waged by al-Qaida was not even an issue in the 2000 presidential campaign strongly suggests that the political will to declare and fight this war didn't exist before September 11," Freeh wrote in the Wall Street Journal on Monday.
"They didn't know that 9/11 was going to happen," Richard Ben-Veniste, another Democratic member of the September 11 commission, told CNN.
But it seemed the memo author "was alerting to the president to the possibility that the strike that we were all anticipating in the summer of 2001 might well occur within the United States," and not abroad as many expected.
Ben-Veniste also said that "sharp questioning or focussed questioning" on the September 11 panel "is not an indication of partisanship. It is an indication of our determination to bring the truth forward."