But soon after Alberto R. Gonzales’s arrival as attorney general in February 2005, the Justice Department issued another opinion, this one in secret. It was a very different document, according to officials briefed on it, an expansive endorsement of the harshest interrogation techniques ever used by the Central Intelligence Agency.

The new opinion, the officials said, for the first time provided explicit authorization to barrage terror suspects with a combination of painful physical and psychological tactics, including head-slapping, simulated drowning and frigid temperatures.

Mr. Gonzales approved the legal memorandum on “combined effects” over the objections of James B. Comey, the deputy attorney general, who was leaving his job after bruising clashes with the White House. Disagreeing with what he viewed as the opinion’s overreaching legal reasoning, Mr. Comey told colleagues at the department that they would all be “ashamed” when the world eventually learned of it.

Later that year, as Congress moved toward outlawing “cruel, inhuman and degrading” treatment, the Justice Department issued another secret opinion, one most lawmakers did not know existed, current and former officials said. The Justice Department document declared that none of the C.I.A. interrogation methods violated that standard.

The classified opinions, never previously disclosed, are a hidden legacy of President Bush’s second term and Mr. Gonzales’s tenure at the Justice Department, where he moved quickly to align it with the White House after a 2004 rebellion by staff lawyers that had thrown policies on surveillance and detention into turmoil.

Congress and the Supreme Court have intervened repeatedly in the last two years to impose limits on interrogations, and the administration has responded as a policy matter by dropping the most extreme techniques. But the 2005 Justice Department opinions remain in effect, and their legal conclusions have been confirmed by several more recent memorandums, officials said. They show how the White House has succeeded in preserving the broadest possible legal latitude for harsh tactics.

A White House spokesman, Tony Fratto, said Wednesday that he would not comment on any legal opinion related to interrogations.

This article is by Scott Shane, David Johnston and James Risen
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A senior administration official called Mr. Bradbury’s active role in shaping legislation and speaking to Congress and the press “entirely appropriate” and consistent with past practice. The official, who spoke on the condition of anonymity, said Mr. Bradbury “has played a critical role in achieving greater transparency” on the legal basis for detention and surveillance programs.

Though President Bush repeatedly nominated Mr. Bradbury as the Office of Legal Counsel’s assistant attorney general, Democratic senators have blocked the nomination. Senator Durbin said the Justice Department would not turn over copies of his opinions or other evidence of Mr. Bradbury’s role in interrogation policy.

“There are fundamental questions about whether Mr. Bradbury approved interrogation methods that are clearly unacceptable,” Mr. Durbin said.

John D. Hutson, who served as the Navy’s top lawyer from 1997 to 2000, said he believed that the existence of legal opinions justifying abusive treatment is pernicious, potentially blurring the rules for Americans handling prisoners.

“I know from the military that if you tell someone they can do a little of this for the country’s good, some people will do a lot of it for the country’s better,” Mr. Hutson said. Like other military lawyers, he also fears that official American acceptance of such treatment could endanger Americans in the future.