WASHINGTON -- Former Vice President Al Gore, charging that President Bush's record on civil liberties poses a "grave danger" to America's constitutional freedoms, urged Monday the appointment of a special counsel to investigate Bush's authorization of warrantless domestic surveillance by the National Security Agency.

In a detailed and impassioned speech sponsored by liberal and conservative groups, Gore said that while much remains unknown about the spying program, "What we do know virtually compels the conclusion that the president of the United States has been breaking the law, repeatedly and insistently."

Gore, the Democratic nominee against Bush in the bitterly disputed 2000 presidential race, also said Congress "should hold comprehensive hearings into these serious allegations of criminal behavior on the part of the president."

White House officials declined to respond to Gore's speech. Tracey Schmitt, a spokeswoman for the Republican National Committee, said the speech demonstrated Gore's "lack of understanding of the threats facing America."

She added: "While the president works to protect Americans from terrorists, Democrats deliver no solutions of their own, only diatribes laden with inaccuracies and anger."

Since acknowledging in December the existence of the surveillance program, Bush has said it targeted only Americans linked to terrorists and "is fully consistent with my constitutional responsibilities and authorities."

Bush said that his constitutional power as commander in chief and the congressional resolution authorizing him to use military force in response to the Sept. 11 terrorist attacks provided a legal basis for the espionage activities.

Many Democrats and some Republicans have disputed those assertions, and the nonpartisan Congressional Research Service, in a study released earlier this month, questioned the surveillance's legality.

The Senate Judiciary Committee has scheduled hearings on the NSA program. The authority to appoint a special prosecutor rests with Attorney General Alberto Gonzales, a longtime Bush aide who, the president has said, is among those who regularly review the spying program.

Gore said a special counsel was needed because of Gonzales' "obvious conflict of interest" in investigating the program's legality.

The speech was the latest in a series harshly critical of Bush policies that Gore has delivered in recent years.

When the former vice president left Monday's speech, some of the 50 supporters who surrounded his car chanted "Gore in '08."

Gore's speech, delivered to an enthusiastic audience at DAR Constitution Hall, was co-sponsored by the left-leaning American Constitution Society for Law and Policy and The Liberty Coalition, a recently formed alliance of groups concerned with privacy and civil liberties. The coalition includes liberal organizations, such as MoveOn.org Political Action, and conservative ones, such as the National Taxpayers Union, the Free Congress Foundation and the American Conservative Union.

"An executive who arrogates to himself the power to ignore the legitimate legislative directives of the Congress or to act free of the check of the judiciary becomes the central threat the Founders sought to nullify in the Constitution -- an all-powerful executive too reminiscent of the king from whom they had broken free," Gore said.

Gore did not specifically call for Bush's impeachment -- an unlikely occurrence in a Congress where both chambers are controlled by Republicans. But he repeatedly argued that Bush's authorization of the domestic surveillance and other administration assertions of executive authority in the struggle against terror threatened "the rule of law" -- the same phrase House Republicans stressed in their impeachment case against President Clinton.

Ranging beyond the spying program, Gore charged that Bush has "brought our republic to the brink of a dangerous breach in the fabric of the Constitution" through many of his tactics in the war on terror.

Gore criticized the administration's indefinite detention of terrorism suspects and the authorization of aggressive questioning techniques for captives that, Gore said, "plainly constitute" torture.

If the president has the power "to eavesdrop on American citizens without a warrant, imprison citizens on his own declaration, kidnap and torture, then what can't he do?" Gore asked.

Gore drew some of his loudest applause when he argued that Congress has become "entirely subservient to the executive branch" and failed to exercise its oversight responsibilities on Bush. He said congressional Democratic leaders briefed on the spying program "must share the blame" with Republicans for not protesting it.

Gore was scheduled to be introduced via a satellite feed by former Rep. Bob Barr, R-Ga., one of the managers of the House impeachment case against Clinton. But problems with a satellite link prevented Barr from speaking.

Barr, a conservative known for his staunch support for civil liberties, has been critical of the administration's surveillance program.