Pulling out "would hand Iraq over to enemies who have pledged to attack us," he said in excerpts of prepared remarks from a speech to the nation.
Mr. Bush's Oval Office address tops off an 18-day span in which the president made five speeches conceding setbacks in Iraq. At the same time, he is outlining a strategy he says will enable the Iraqi people to establish a stable political system and a strong defense capable of quelling a stubborn insurgency.
(CBS will broadcast the speech live at 9 p.m. eastern time. Bob Schieffer will anchor from Washington.)
The speech comes at a time when the president has sparked a national furor over security versus civil liberties. Mr. Bush acknowledged Saturday that on more than 30 occasions he secretly authorized the National Security Agency to spy on Americans and other residents and defiantly vowed to continue such domestic eavesdropping "for as long as our nation faces a continuing threat from al Qaeda and related groups."
Mr. Bush's unusually frank admission, made in his weekly radio address, came amid a bipartisan uproar in Congress after The New York Times revealed the secret NSA program in Friday's editions.
CBS News correspondent Bill Plante reports Mr. Bush lashed out at news organizations for making the story public. Mr. Bush said the report relied on unauthorized disclosure of classified information that "damages our national security and puts our citizens at risk." Disclosure of the program helped generate opposition to a renewal of the Patriot Act in the Senate on Friday.
"The activities I have authorized make it more likely that killers like these 9/11 hijackers will be identified and located in time," Mr. Bush said in a rare live address. "And the activities conducted under this authorization have helped detect and prevent possible terrorist attacks in the United States and abroad."
He said congressional leaders have been apprised of the secret order "more than a dozen times."
First Amendment legal expert Floyd Abrams told CBS News correspondent Randall Pinkston the president is attempting to mitigate his sidestepping of Congress by saying he had informed some lawmakers.
"It is mitigated in the sense that Congress was not completely uninformed," Abrams said. "As a legal matter though, what the president has authorized 30 times may have been illegal 30 times."