WASHINGTON, April2 : The Justice Department in 2003 gave military interrogators broad authority to use extreme methods in questioning detainees and argued that wartime powers largely exempted interrogators from laws banning harsh treatment, according to a memorandum publicly disclosed on Tuesday.

In a sweeping legal brief written in March 2003, when the Pentagon was struggling to determine the appropriate limits for its interrogators, the Justice Department gave the Pentagon much of the same authority it had provided to the Central Intelligence Agency in a memorandum months earlier. Both memorandums were later rescinded by the Justice Department.

The disclosure of the 2003 document, a detailed 81-page opinion written by John C Yoo, who at the time was the second-ranking official at the Office of Legal Counsel at the Justice Department, is likely to fuel the already intense debate about legal boundaries in the face of a continuing terrorist threat.

Yoo’s memorandum is the latest document to illuminate the legal foundation that Bush administration lawyers used after the attacks of September 11, 2001, to give the White House broad powers to capture, detain and interrogate suspects around the globe.

The thrust of Yoo’s brief has long been known, but its specific contents were revealed on Tuesday after government lawyers turned it over to the American Civil Liberties Union, which has sought hundreds of documents from the Bush administration under the Freedom of Information Act.

Some legal scholars said on Tuesday that they were amazed at the scope of the memorandum.

“This is a monument to executive supremacy and the imperial presidency,” said Eugene R Fidell, who teaches military justice at Yale Law School and the Washington College of Law at American University. “It’s also a road map for the Pentagon for fending off any prosecutions.”

The memorandum gave the military broad latitude to use harsh interrogation methods. It reasoned that federal laws prohibiting assault were not applicable to military interrogators dealing with members of al-Qaeda because of White House authority during wartime. It also argued that many American and international laws would not apply to interrogations overseas.

“Even if an interrogation method arguably were to violate a criminal statute, the Justice Department could not bring a prosecution because the statute would be unconstitutional as applied in this context,” it reads.

Justice Department lawyers later rescinded both Yoo’s memorandum and the similar one written for the CIA in August 2002.

In a book published last year, Jack Goldsmith, who as head of the Office of Legal Counsel made the decision to rescind the memorandums, criticised the documents, saying they had used careless legal reasoning to provide national security agencies with interrogation authority.

Written to William J Haynes II, who at the time was the Pentagon’s general counsel, Yoo’s document was meant to give legal guidance to Defence Department lawyers as they wrestled with a list of interrogation methods for prisoners at the military prison at Guantanamo Bay, Cuba.

The document explains that Haynes had asked the Justice Department “to examine the legal standards governing military interrogations of alien unlawful combatants held outside the United States”.

The Pentagon was trying to set clear guidelines for military interrogators after Donald H Rumsfeld, the defence secretary at the time, withdrew approval for some interrogation techniques opposed by some senior military lawyers.

Ultimately, Yoo’s memorandum provided the legal foundation for the group’s final report, which defended the use of harsh interrogation methods.