(AP) Attorney General Alberto Gonzales defended the Bush administration's domestic spying program Tuesday and suggested that some critics and news reports have misled Americans about the breadth of the National Security Agency's surveillance.

Gonzales said the warrantless surveillance is critical to prevent another terrorist attack within the United States and falls within President Bush's constitutional authority and the powers granted by Congress immediately following the Sept. 11, 2001 terrorist attacks.

At a Georgetown Law School Forum, Gonzales said the nation needs "to remember that ... it's imperative for national security reasons that we can detect reliably, immediately and without delay" any al-Qaida related communication entering or leaving the United States.

As he spoke, more than a dozen students stood silently with their backs turned to the attorney general. Outside the classroom where Gonzales was to speak, a pair of protesters held up a sheet that said, "Don't torture the Constitution."

Gonzales cautioned his listeners about critics and journalists who have mischaracterized details about the program. "Unfortunately, they have caused concern over the potential breadth of what the President has actually authorized," he said.

The attorney general's appearance at the law school is part of a campaign by the Bush administration to overcome criticism, often by attempting to redefine the program.

On Monday at Kansas State University, Bush said the program should be termed a "terrorist surveillance program" and contended it has the backing of legal experts, key lawmakers and the Supreme Court.

But some members of Congress from both parties have questioned whether the warrantless snooping is legal. And many Democrats along with a number of legal experts say flatly that Bush has broken the law and has committed an impeachable offense.

Last week, Gonzales sent leaders of Congress a 42-page legal defense of warrantless eavesdropping which suggests that the Foreign Intelligence Surveillance Act is unconstitutional if it prevents the NSA's warrantless eavesdropping.

The National Security Agency program bypassed the special FISA court Congress established in 1978 to approve or reject secret surveillance or searches of foreigners and U.S. citizens suspected of terrorism or espionage.