Responding to a congressional uproar, the Bush administration said Monday that a secret domestic surveillance program had yielded intelligence results that would not have been available otherwise in the War on Terror.

With Democrats and Republicans alike questioning whether President Bush had the legal authority to approve the program, Attorney General Alberto Gonzales argued that Congress had essentially given Bush broad powers to order the domestic surveillance after the Sept. 11, 2001, attacks.

"Our position is that the authorization to use military force, which was passed by the Congress shortly after Sept. 11, constitutes that authority," Gonzales said. He called the monitoring "probably the most classified program that exists in the United States government."

At a White House briefing and in a round of television appearances, Gonzales provided a more detailed legal rationale for Bush's decision authorizing the National Security Agency to eavesdrop on international phone calls and e-mails of people within the United States without seeking warrants from courts.

He said Bush's authorization requires that at least one of the parties be outside the country and linked to Al Qaeda or an affiliated organization.

But he refused to say how many Americans had been targeted and insisted the eavesdropping was "very limited, targeted" electronic surveillance. "This is not a situation of domestic spying," he said.

Gonzales defended Bush's decision not to seek warrants from the secretive Federal Intelligence Surveillance Court, saying that "we don't have the speed and the agility that we need in all circumstances to deal with this new kind of enemy."

Gen. Michael Hayden, deputy national intelligence director who was head of the NSA when the program began in October 2001, said, "I can say unequivocally we have got information through this program that would not otherwise have been available."

In offering only a glimpse into the program, Hayden said the monitoring would take place for a shorter period of time and be less intrusive than what is normally authorized by the secret surveillance court. Yet he acknowledged that the program is more aggressive than other government monitoring.

The domestic spying revelations has created an uproar in Congress, with Democrats and Republicans calling for investigations.

"They talk about constitutional authority," said Senate Judiciary Chairman Arlen Specter, R-Pa. "There are limits as to what the president can do." He has said he'll hold hearings on the monitoring program early next year.

Gonzales would not say who in Congress was briefed or when, but said that more lawmakers have been told of the program in recent days, including Specter. "We're engaged now in a process of educating the American people ... and educating the American Congress," Gonzales said.

Monday's briefing was the most detailed legal explanation given by an administration officials since the New York Times reported Thursday night that Bush had authorized the NSA to conduct the surveillance after the 9/11 attacks.

"This is just an outrageous power grab," said Sen. Russ Feingold, D-Wis. on NBC's "Today" show. "Nobody, nobody thought when we passed a resolution to invade Afghanistan and to fight the War on Terror ... that this was an authorization to allow a wiretapping against the law of the United States."

Senate Democratic Leader Harry Reid of Nevada also called for an investigation, and House Democratic leaders asked Speaker Dennis Hastert to create a bipartisan panel to do the same.

Bush acknowledged in his weekly radio address Saturday that he had authorized the spying, saying it was a necessary step in the war against terror.

The existence of the NSA program surfaced as Bush was fighting to save the expiring provisions of the USA Patriot Act, the domestic anti-terrorism law enacted after the Sept. 11 attacks.

Renewal of the law has stalled over some its most contentious provisions, including powers granted law enforcement to gain secret access to library and medical records and other personal data during investigations of suspected terrorist activity.