Gonzales' strong defense of Mr. Bush's program was challenged by Republican Sen. Arlen Specter, chairman of the Judiciary Committee, and committee Democrats during sometimes contentious questioning.
Specter told Gonzales that even the Supreme Court had ruled that "the president does not have a blank check." Specter suggested that the program's legality be reviewed by a special federal court set up by the 1978 Foreign Intelligence Surveillance Act.
"There are a lot of people who think you're wrong. What do you have to lose if you're right?" Specter, R-Pa., asked Gonzales.
The attorney general sidestepped the question directly, just saying, "Obviously, we would consider and are always considering methods of fighting the war effectively against al Qaeda."
However, he said that court was already quite familiar with the program. He also said he did not think the 1978 law needed to be modified.
And, said Gonzales, "To end the program now would afford our enemy dangerous and potential deadly new room for operation within our borders."
Specter told Gonzales that federal law "has a forceful and blanket prohibition against any electronic surveillance without a court order."
While the president claims he has the authority to order such surveillance, Specter said, "I am skeptical of that interpretation."
A former Texas judge, Gonzales played an important role as White House counsel in developing the legal justification for the spy program. He served in that post from January 2001 to February 2005.
CBS News correspondent Bob Fuss reports the attorney general is making two arguments, both being sharply questioned, for the president bypassing the law that requires warrants for all wiretaps of Americans' phone calls.
The first is that when Congress authorized all "necessary force" to track down the terrorists after 9/11 that included the right to listen to phone calls; and second, that the U.S. is at war and the president's war powers include the power to spy on the enemy.
"The president is acting with authority both by the Constitution and by statute," Gonzales said.
Committee Democrats, who have generally contended that Mr. Bush is acting illegally in permitting domestic surveillance by the National Security Agency, sharply grilled Gonzales.
Sen. Patrick Leahy, D-Vt., asked if the authorization Mr. Bush claims to have would also enable the government to open mail — in addition to monitoring voice and electronic communications.
"There is all kinds of wild speculation out there about what the president has authorized and what we're actually doing," Gonzales said.
"You're not answering my question," Leahy retorted. "Does this law authorize the opening of first class mail of U.S. citizens? Yes or no."
"That's not what's going on," Gonzales said. "We are only focusing on international communications, where one part of the conversation is al Qaeda."