National Security Advisor Condoleezza Rice says the Bush administration understood the threat posed by al-Qaida before the September 11, 2001 terrorist attacks, and made the elimination of the network a high priority.
In sworn testimony to the independent commission investigating the attacks, Ms. Rice said that in the first months of his administration, President Bush moved to develop a new and comprehensive strategy to destroy al-Qaida.
She said that strategy, approved on September 4, aimed to end al-Qaida's foreign sanctuaries and directed the CIA to prepare an aggressive cover program to disrupt the network.
She also said in the summer of 2001, new threat information put the United States on a heightened state of alert, but the intelligence was vague.
She says despite the administration's efforts, there was no silver bullet that could have prevented the September 11 attacks.
During her two-and-a-half hour sworn testimony, Ms. Rice is expected to be questioned by the 10-member panel on allegations from former counterterrorism chief Richard Clarke, who says the Bush administration did not make terrorism an urgent priority before the September 11 attacks.
Ms. Rice is also expected to dispute Mr. Clarke's assertions that the administration made Iraq too much of a priority after the attacks.
Ms. Rice's appearance is being broadcast live by the major U.S. television networks and overseas by Voice of America.
The commission's chairman, Republican Thomas Kean, has said he wants Ms. Rice to clear up what he calls "discrepancies" in some of her public statements about the September 11 attacks.
President Bush and Vice President Cheney have agreed to meet jointly and in private with the panel. Mr. Bush said earlier this week he looks forward to sharing information with the commission. He also defended his record, saying he immediately went to war against al-Qaida after the September 11 attacks.