The US president was responding to criticism on Thursday after a newspaper report alleged that the National Security Agency (NSA) had access to billions of phone calls made by American citizens.
Bush said that any intelligence activities he had authorised were legal and that the government was not eavesdropping on phone calls without court approval.
"The privacy of ordinary Americans is fiercely protected in all our activities," Bush said at a hastily called press briefing. "We're not mining or trolling through the personal lives of millions of innocent Americans."
The White House also criticised this latest leak to the media regarding intelligence, suggesting it could hinder the fight against terrorism.
"As a general matter, every time sensitive intelligence is leaked, it hurts our ability to defeat this enemy," Dana Perino, the White House spokeswoman, said.
The USA Today newspaper reported that the NSA was amassing a database that used records provided by three major US phone companies - AT&T, Verizon and BellSouth.
But the newspaper said the NSA was not listening to or recording phone conversations.
USA Today said calls originating and terminating within the United States had also been included in the database.
Questions are being asked over
This contradicts a declaration by the president last year that eavesdropping only applied to communications from inside the US to overseas.
The paper quoted one source as saying: "It's the largest database ever assembled in the world."
The NSA wants the database of domestic call records to look for any patterns that might suggest terrorist activity, USA Today said.
The claims have provoked some Democrats to suggest that the confirmation of Air Force General Michael Hayden as the new director of the CIA could be complicated.
Hayden was head of the NSA between 1999 and 2005 and USA Today said he would have overseen the call-tracking programme.
Senator Patrick Leahy of Vermont said he was shocked by the revelations, declaring that "it is our government, it's not one party's government. It's America's government. Those entrusted with great power have a duty to answer to Americans what they are doing."
The White House played down the controversy, saying the nomination of Hayden was going "full steam ahead."
"We're not mining or trolling through the personal lives of millions of innocent Americans"
George Bush, the US president
Hayden proceeded with meetings with individual senators who will be considering his nomination.
The NSA and phone companies declined to comment at length on the report.
Don Weber, the NSA spokesman, said it would be "irresponsible to comment on actual or alleged operational issues," but added: "It is important to note that NSA takes its legal responsibilities seriously and operates within the law."
Jeff Battcher, BellSouth spokesman, said: "To the best of our knowledge, the NSA has not requested any confidential customer information from BellSouth in the last several years."