Months after the September 11, 2001 terror attacks, President Bush signed an order giving the National Security Agency authorization to eavesdrop on Americans and other people in the United States to look for evidence of potential terrorist activity without first obtaining search warrants.

According to a New York Times report, the presidential order, signed in 2002, has given the agency the right to monitor international phone calls and international e-mails of hundreds, maybe even thousands of people inside the United States in a search for ties to "dirty numbers" potentially linked to the al Qaeda terror network. The targets included U.S. citizens, permanent legal residents, tourists and other foreigners, raising serious concerns within the administration — and from the few members of Congress who knew about it — over whether the order crossed legal boundaries and trampled civil liberties.

Speaking to almost a dozen current and former administration officials who requested anonymity because of the classified nature of the program, the report describes how the NSA eavesdropped on as many as 500 people inside the U.S. at any given time without warrants and monitored as many as 7,000 people suspected of terrorist ties overseas at one time. The program grew out of concerns after the September 11 attacks that the nation's intelligence-gathering agencies were not equipped to effectively deal with the al Qaeda threat because of legal and bureaucratic restrictions, leading President Bush to sign an executive order relaxing some of those restrictions.

Prior to this program, the NSA — the nation's largest and most secretive intelligence agency, nicknamed "No Such Agency" — typically obtained court orders for its domestic surveillance, which was mostly limited to foreign embassies and missions. In the past, the NSA's mission was normally to break codes and maintain listening posts around the world to spy on foreign governments, diplomats, drug lords and terrorists, but not within U.S. borders.

While some government officials said the program uncovered several planned terrorist plots — such as the one by Iyman Faris, an Ohio trucker who pleaded guilty in 2003 to supporting al Qaeda by planning to destroy the Brooklyn Bridge — there were some NSA officials who were so concerned about whether the operation crossed constitutional limits on legal searches that they would not participate, according to the Times. The agency also reportedly uncovered what appeared to be an al Qaeda plot to attack British pubs and train stations with fertilizer bombs, but officials said most people targeted by the program have never been charged with a crime.

The administration views the operation as necessary in order to allow the NSA to move quickly to monitor communications that may have information about threats to the U.S.

"This is really a sea change," a former senior official who specializes in national security law told the paper. "It's almost a mainstay of this country that the NSA only does foreign searches." Among those expressing concern were 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.

Concerns over the legality of the program led the administration to temporarily suspend it last year and impose tighter restrictions on who could be surveilled. Administration officials said they are confident that the safeguards in the system are sufficient to protect the privacy and the civil liberties of Americans and that, in some cases, the Justice Department eventually seeks a warrant if it wants to expand the eavesdropping to include communications that occur only within the U.S.

The revelation comes just days after an "NBC Nightly News" report that the Pentagon has been compiling a secret database of 1,500 "suspicious incidents" across the U.S. over a 10-month period that included four dozen anti-war meetings and protests (see "If You Oppose The War, The Pentagon May Already Have Your Number").

The White House — which has been stung by a series of major leaks about secret intelligence programs, including a recent Washington Post expose about secret overseas CIA jails (see "Report Of 'Covert' CIA Jail Sparks Human-Rights Investigation") — asked the Times not to publish the article, saying that it could jeopardize ongoing investigations and alert would-be terrorists that they might be under scrutiny. After meeting with senior administration officials, the paper said it agreed to delay publication of the piece for a year to conduct additional reporting.

Widespread abuses of warrantless eavesdropping in the past, such as the surveillance of Vietnam War protesters and civil-rights activists that became public in the 1970s, led to passage of the Foreign Intelligence Surveillance Act, which imposes strict limits on intelligence gathering on American soil. Among its provisions is one requiring search warrants for wiretaps in national security cases.

— Gil Kaufman

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