James Comey, a deputy to then-Attorney General John Ashcroft, questioned legality of the NSA program and refused to extend it in 2004. White House aides then turned to Ashcroft while the attorney general was hospitalized for gallbladder surgery, but Ashcroft, author of the controversial USA Patriot Act, also refused to endorse the spyhing.

"This is a limited program designed to prevent attacks on the United States of America," Bush claimed after visiting wounded troops at Brooke Army Medical Center in San Antonio. But with mountain evidence showing otherwise, calls increased for a Senate inquiry into spying on Americans.

The NSA program "listens to a few numbers called from the outside of the United States and of known al Qaeda or affiliate people," he said. "If somebody from al Qaeda is calling you, we'd like to know why," Bush said.

White House spokesman Trent Duffy later said that while the president focused on calls being made from abroad, the eavesdropping program was also conducted on communications originating from inside the United States.

"We're at war," Bush said. "I've got to use the resources at my disposal, within the law, to protect the American people. And that's what we're doing."

Democratic Sen. Charles Schumer of New York, a member of the Judiciary Committee, said he would ask committee Chairman Sen. Arlen Specter, a Pennsylvania Republican, to seek testimony from Comey, Ashcroft, Attorney General Alberto Gonzales and White House Chief of Staff Andrew Card.

"Today's revelations really heighten concerns about this," Schumer said on "Fox News Sunday."

Capitol Hill Blue revealed last year that Bush authorized the NSA to monitor, without court approval, the international telephone calls and e-mails of U.S. citizens suspected of links to foreign terrorists. The New York Times knew about the spying last year as well but withheld the story under pressure from the White House, choosing instead to publish the information two weeks ago.

A 1978 law, the Foreign Intelligence Surveillance Act, makes it illegal to spy on U.S. citizens in the United States without the approval of a special court.

Schumer said if the president thought the law hampered the war on terrorism he should have asked Congress to consider making changes.

In an attempt to divert attention away from the legal questions surrounding the spying, Republican Sen. Mitch McConnell of Kentucky said on "Fox News Sunday" that Congress should focus on investigating who in the U.S. government leaked the existence of the program.

The Senate Intelligence Committee, which usually meets in closed session, would be a better place than the judiciary panel to investigate the program, McConnell said.

Comey's refusal to reauthorize the NSA program prompted Card and Gonzales to try to get approval from Ashcroft in March 2004 while he was in a Washington hospital for gallbladder surgery.

Ashcroft also refused to give his authorization to continue with aspects of the program.

But the Bush administration went ahead with the program without approval from the nation's top law enforcement officials.