"Hypotheticals are different from real life, and in any legal opinion the actual facts and circumstances are critical," Mukasey said in a written answer to Democrats on the committee.

Mukasey offered a similar response in his October 18 confirmation hearing

Human rights groups consider waterboarding -- in which prisoners are strapped down and either dunked in water or have water poured over them in order to produce the sensation of drowning -- a form of torture.

It was specifically banned in a 2006 law passed by Congress.

Bush has acknowledged authorizing the use of "alternative" interrogation techniques against suspected terrorists.

Though his administration insists that it does not torture prisoners, it refuses to reveal which interrogation techniques may be used.

"When we find somebody who may have information regarding a potential attack on America, you bet we're going to detain them and you bet we're going to question them, because the American people expect us to find out information, actionable intelligence, so we can help them -- help protect them," Bush said earlier this month.

He said his administration sticks to "U.S. law and our international obligations," adding that "the techniques that we use have been fully disclosed to appropriate members of the United States Congress."

Mukasey's refusal to declare waterboarding to be torture has boosted opposition to his nomination.

Sen. Sheldon Whitehouse, D-Rhode Island -- who raised the issue during the Judiciary Committee hearing -- called Mukasey's answer a "massive hedge," and three Democratic presidential candidates have cited it as a reason to oppose his confirmation.

The top Republican on the Judiciary Committee, Sen. Arlen Specter of Pennsylvania, urged Mukasey last week to clarify his response to questions about waterboarding and the president's authority to order electronic surveillance.

Sen. Patrick Leahy, D-Vermont and the committee's chairman, said he remains very concerned that the retired federal judge "finds himself unable to state unequivocally that waterboarding is illegal and below the standards and values of the United States."

"I await his response to other written questions and letters from Republican and Democratic senators that were sent to him last week, and I will consult with Sen. Specter and other members of the Judiciary Committee before scheduling committee consideration of this nomination," Leahy said.

Waterboarding is not being used as part of its interrogations now, sources with knowledge of the CIA-run interrogation program have said.

But it was used in the interrogation of Khalid Shaikh Mohammed, who is facing trial for planning al Qaeda's 2001 attacks on New York and Washington, the sources have said.

In Tuesday's letter, Mukasey restated his belief that the Constitution and federal law bar the president from ordering the use of torture.

He said the techniques Democratic senators described to him "seem over the line or, on a personal basis, repugnant to me, and would probably seem the same to many Americans."

Mukasey promised to review any "coercive interrogation techniques" used by U.S. intelligence operatives once confirmed.

If he determines them to be torture, "I will not hesitate to so advise the president and will rescind or correct any legal opinion of the Department of Justice that supports use of the technique," he told the senators.