WASHINGTON, Dec. 15 - Months after the Sept. 11 attacks, President Bush secretly authorized the National Security Agency to eavesdrop on Americans and others inside the United States to search for evidence of terrorist activity without the court-approved warrants ordinarily required for domestic spying, according to government officials.
Under a presidential order signed in 2002, the intelligence agency has monitored the international telephone calls and international e-mail messages of hundreds, perhaps thousands, of people inside the United States without warrants over the past three years in an effort to track possible "dirty numbers" linked to Al Qaeda, the officials said. The agency, they said, still seeks warrants to monitor entirely domestic communications.
The previously undisclosed decision to permit some eavesdropping inside the country without court approval was a major shift in American intelligence-gathering practices, particularly for the National Security Agency, whose mission is to spy on communications abroad. As a result, some officials familiar with the continuing operation have questioned whether the surveillance has stretched, if not crossed, constitutional limits on legal searches.
"This is really a sea change," said a former senior official who specializes in national security law. "It's almost a mainstay of this country that the N.S.A. only does foreign searches."
Nearly a dozen current and former officials, who were granted anonymity because of the classified nature of the program, discussed it with reporters for The New York Times because of their concerns about the operation's legality and oversight.
According to those officials and others, reservations about aspects of the program have also been expressed by Senator John D. Rockefeller IV, the West Virginia Democrat who is the vice chairman of the Senate Intelligence Committee, and a judge presiding over a secret court that oversees intelligence matters. Some of the questions about the agency's new powers led the administration to temporarily suspend the operation last year and impose more restrictions, the officials said.
The Bush administration views the operation as necessary so that the agency can move quickly to monitor communications that may disclose threats to the United States, the officials said. Defenders of the program say it has been a critical tool in helping disrupt terrorist plots and prevent attacks inside the United States.
Administration officials are confident that existing safeguards are sufficient to protect the privacy and civil liberties of Americans, the officials say. In some cases, they said, the Justice Department eventually seeks warrants if it wants to expand the eavesdropping to include communications confined within the United States. The officials said the administration had briefed Congressional leaders about the program and notified the judge in charge of the Foreign Intelligence Surveillance Court, the secret Washington court that deals with national security issues.
The White House asked The New York Times not to publish this article, arguing that it could jeopardize continuing investigations and alert would-be terrorists that they might be under scrutiny. After meeting with senior administration officials to hear their concerns, the newspaper delayed publication for a year to conduct additional reporting. Some information that administration officials argued could be useful to terrorists has been omitted.
Dealing With a New Threat
While many details about the program remain secret, officials familiar with it say the N.S.A. eavesdrops without warrants on up to 500 people in the United States at any given time. The list changes as some names are added and others dropped, so the number monitored in this country may have reached into the thousands since the program began, several officials said. Overseas, about 5,000 to 7,000 people suspected of terrorist ties are monitored at one time, according to those officials.
Several officials said the eavesdropping program had helped uncover a plot by Iyman Faris, an Ohio trucker and naturalized citizen who pleaded guilty in 2003 to supporting Al Qaeda by planning to bring down the Brooklyn Bridge with blowtorches. What appeared to be another Qaeda plot, involving fertilizer bomb attacks on British pubs and train stations, was exposed last year in part through the program, the officials said. But they said most people targeted for N.S.A. monitoring have never been charged with a crime, including an Iranian-American doctor in the South who came under suspicion because of what one official described as dubious ties to Osama bin Laden.