WASHINGTON -- 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.

    Attorney General Alberto Gonzales said Congress had essentially given President Bush the authority for domestic surveillance after the Sept. 11 attacks.

    At a White House briefing and in a round of television appearances, Gonzales provided a more detailed legal rationale for President 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 refused to say how many people had been targeted and insisted, "This is not a situation of domestic spying."

    Gonzales defended Bush's decision not to seek warrants from the 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, said, "I can say unequivocally we have got information through this program that would not otherwise have been available."

    Gonzales said he had begun meeting with members of Congress on the Bush administration's view that Congress' authorization of the use of military force after the Sept. 11, 2001 attacks was ample authorization for the surveillance.

    "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.

    It was the most detailed legal explanation given by an administration officials since the New York Times reported Thursday that since October 2001 Bush had authorized the NSA to conduct the surveillance.

    Gonzales said Congress' action after Sept. 11 essentially "does give permission for the president of the United States to engage in this kind of very limited, targeted electronic surveillance against our enemy."

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

    "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."

    Democrats and Republicans called separately Sunday for congressional investigations into the domestic spying.

    Sen. Arlen Specter, R-Penn., chairman of the Senate Judiciary Committee, said Sunday he intends to hold hearings.

    "They talk about constitutional authority," Specter said. "There are limits as to what the president can do."

    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