WASHINGTON -- A newly disclosed Justice Department legal memo, written in March 2003 and authorizing the military's use of extremely harsh interrogation techniques, offers what could be a revealing clue in an unsolved mystery: What responsibility did top Pentagon and administration officials have for abuses committed by American troops at the Abu Ghraib prison in Iraq and in Afghanistan, at Guantanamo Bay, Cuba, and elsewhere?
Some legal experts and advocates said yesterday that the memo, written the month that the United States invaded Iraq, adds to evidence that the abuse of prisoners in military custody may have involved signals from higher officials and not just irresponsible actions by low-level personnel.
The memo was written by John C. Yoo, of the Office of Legal Counsel, the executive branch's highest authority on the interpretation of the law. It told the Pentagon's senior leadership that inflicting pain on a suspect would not be considered torture unless it caused "death, organ failure or permanent damage" and was the most fully developed legal justification that has yet come to light for inflicting physical and mental pressure on suspects.
While resembling an August 2002 memo drafted largely by Yoo, the March 2003 opinion went further, arguing more explicitly that the president's war powers could trump the law against torture, which it said could not constitutionally be enforced if it interfered with the commander in chief's orders.
Scott L. Silliman, head of the Center on Law, Ethics and National Security at Duke University and a former Air Force lawyer, said he did not believe the Justice Department memo directly caused mistreatment. But he added, "The memo helped to build a culture that, in the absence of leadership from the highest ranks of the Pentagon, allowed the abuses at Abu Ghraib and elsewhere."
Silliman said that because opinions issued by the Office of Legal Counsel are "binding on the Defense Department," Yoo's opinion effectively sidelined military lawyers who strongly opposed harsh interrogation methods.
In an e-mail message, Yoo, now a Berkeley law professor, rejected the idea that his memo helped create a culture for mistreatment.
"The 'culture of abuse' theory has no reliable evidence to support it," Yoo wrote. He noted that several military investigations found that what he called "the appalling abuses" at Abu Ghraib were not authorized by any military policy.
"While each case of abuse is regrettable, it is not possible for a large organization charged with protecting the national security, under extraordinary pressure, to perform its mission error-free," Yoo said.
Top Pentagon officials, including Donald H. Rumsfeld, the former defense secretary, have said that they never condoned the mistreatment of prisoners. But the role played by senior military and civilian officials at the Pentagon has never been fully explained, and it is not clear how the legal memo, which was addressed to William Haynes, then the top Pentagon lawyer, influenced interrogation practices.
Several Democratic lawmakers asserted Wednesday that the memo led directly to the abuses of detainees at Abu Ghraib, although the memo specifies that it applies only to "unlawful combatants," a label that would not apply to the largely Iraqi population captured during the Iraq war.
The memo did apply to all unlawful combatants detained outside the United States, at a time when the Pentagon was struggling with the rules for interrogations of detainees held at Guantanamo Bay and in other places, like Afghanistan.
William C. Banks, a specialist on national security law at Syracuse University, said that the memo shed critical light on the Bush administration but that it was "far fetched" to think it might be used to overturn convictions of soldiers for abuse at Abu Ghraib or elsewhere.
The memo was made public Tuesday after it was declassified in response to a request by the American Civil Liberties Union under the Freedom of Information Act.
Both the August 2002 and March 2003 memos were formally withdrawn by the Justice Department in 2004, after Yoo's successors at the Office of Legal Counsel concluded that the memos went too far.
Jonathan Hafetz, a lawyer representing Ali al-Marri, a Qatar citizen arrested in the United States after the Sept. 11 attacks, said he believed the March 2003 memo explains why his client was removed from the criminal justice system and placed in a military jail in Charleston, S.C., in June 2003.