Can the government spy on citizens without a warrant?

President Bush's decision to allow the super-secret National Security Agency to spy on Americans without court warrants has touched off stormy debate about his aggressive approach to the war on terror.

This clash - between civil libertarians and the administration's expansive view of presidential power - is a recurring theme in the Bush White House. It lies at the center of ongoing debates over the government's use of coercive interrogation techniques and the open-ended detention of alleged enemy combatants at Guantánamo Bay, Cuba, and in military prisons in the United States.

This week, the spotlight is on a recently disclosed classified operation that permits the NSA to monitor communications between suspected Al Qaeda members overseas and American citizens in the US. It is being done without first obtaining a warrant from a special intelligence court set up to police such sensitive intercepts.

Instead of following the safeguards established by Congress under the 1978 Foreign Intelligence Surveillance Act (FISA), Bush administration lawyers concluded that the White House could sidestep the warrant requirements while conducting the espionage operation.

Critics say the secret spying is illegal and an abuse of the president's constitutional authority. Supporters say Bush is well within his power to protect the nation from terrorists.

Disclosure of the NSA operation by the New York Times last Friday surprised many members of Congress and is said to have complicated efforts to reauthorize the Patriot Act. Republican Sen. Arlen Specter, chairman of the Judiciary Committee, has called for hearings to look into the NSA operation. Supreme Court nominee Samuel Alito has been warned to prepare for close questioning on the matter in his upcoming confirmation hearing. And there is talk of the possible appointment of two special counsels, one to look into the legality of the NSA operation, the other to investigate the disclosure of the classified project to the Times.

In addition, Sen. Barbara Boxer (D) of California has asked legal scholars to research whether Bush's authorization of secret spying is an impeachable offense.

President Bush and other administration officials have sought to blunt the barrage of criticism by emphasizing the exigencies of protecting the nation from terrorists. They stress that despite the highly classified nature of the operation, the White House briefed key members of Congress about the ongoing covert effort.

But some members of Congress say they were given few details and were unable to effectively exercise oversight responsibilities after being sworn to secrecy.

Administration officials also notified the chief judge of the Foreign Intelligence Surveillance Court, which is empowered to authorize warrants for such spying.

One section of the foreign intelligence law, FISA, authorizes warrantless surveillance under limited circumstances - but it does not appear to apply to the NSA operation as described by administration officials. Neither President Bush nor Attorney General Alberto Gonzales is claiming the secret operation was conducted in compliance with FISA.

Instead, they say the operation was carried out under President Bush's constitutional power as commander in chief, and under Congress's Joint Authorization for Use of Military Force, which was passed more than four years ago, shortly after the 9/11 attacks.

The administration made the same argument before the US Supreme Court in the case of alleged enemy combatant Yaser Hamdi. The court declined to address the president's power as commander in chief. Instead, it based its June 2004 decision upholding Mr. Hamdi's military detention solely on the congressional authorization argument. But given the splintered posture of the high court in that case and the possible arrival of a second new justice, the potential outcome in any future case is less than clear.

"It is a murky area," says Ruth Wedgwood, an international law professor at Johns Hopkins University.

"It is an area in which Congress has legislated but, to be sure, they didn't anticipate Al Qaeda in 1978," she says. "It is also an area where obviously Americans have high expectations about their privacy."

FISA was enacted to prevent domestic surveillance abuses that occurred during earlier administrations, including the Nixon White House.

Should the debate make it into a courtroom, at issue will be whether FISA preempts the president from taking actions as commander in chief in the war on terror that ignore or violate the surveillance statute.

"The president is simply off the rails," says Marc Rotenberg, executive director of the Electronic Privacy Information Center, which closely monitors surveillance issues. Mr. Rotenberg says Bush's reliance on the commander-in-chief powers "is probably overly broad and will be rejected."

David Rivkin, a Washington lawyer and former Reagan and Bush I administration official, has a different perspective. "FISA was designed to deal with essentially peacetime counterintelligence and counterterrorism operations," he says. "We are now at war."

He says Bush's secret NSA operation is "tantamount to trying to break Japanese military codes or intercept German communications during World War II." The FISA requirement of judicial oversight of secret intelligence operations would mandate a war-fighting role for judges that the Constitution does not authorize, Mr. Rivkin says. "Where is it written in the Constitution that the president is supposed to exercise his commander-in-chief power based upon what a judge says or doesn't say?"