President Bush says the federal government's monitoring of telephone activity is limited to instances where authorities believe terrorists are making calls to or from the United States.
Mr. Bush's comments follow a newspaper report that major U.S. telephone companies have given the National Security Agency records of customer telephone calls.
President Bush says, following the September 11, 2001 terrorist attacks on the United States, he authorized the National Security Agency to intercept the international communications of people with known links to al-Qaida and other terrorist groups, adding, in his words, "We want to know what they are saying."
But, speaking from the White House before departing on a trip to the U.S. Gulf Coast, Mr. Bush stressed that the program's sole aim is to prevent terrorism, and said it does not violate U.S. law.
"The privacy of ordinary Americans is fiercely protected in all our activities. We are not 'mining' or 'trolling' through the personal lives of millions of innocent Americans. Our efforts are focused on links to al-Qaida and their known affiliates."
Mr. Bush did not confirm or deny that the government has obtained domestic telephone records, nor did he comment on how those records might be used to further the battle against terrorism Earlier, the "USA Today" newspaper cited anonymous sources as saying that the National Security Agency had secured records from America's largest telephone companies, none of which are state owned.
The article said the federal government is not attempting to construct a database of all telephone conversations within the United States, but rather looking for calling patterns that might indicate terrorist communications.
In his remarks, President Bush said the U.S. government does not listen to domestic phone calls without court approval, and that members of Congress have been briefed on the program.
But several prominent Republican and Democratic legislators have expressed surprise and dismay about the corporations surrendering their records to federal authorities, and urged closer examination of the practice.
A prime defender of the government's anti-terrorism domestic surveillance program is newly designated CIA director nominee Michael Hayden, a former director of the National Security Agency.
General Hayden is expected to face sharp questions about the program at his Senate confirmation hearing.
Civil rights groups have blasted the program as an infringement on Americans' liberty and right to privacy.