WASHINGTON — The Pentagon in the aftermath of the terrorist attacks of September 11, 2001, pursued abusive interrogation techniques once used by North Korea and Vietnam on American POWs despite stern warnings by several military lawyers that the methods were cruel and even illegal, according to a Senate investigation.

The findings, detailed in a hearing yesterday, brought rebukes of the Pentagon effort from Democrats and Republicans alike.

“The guidance [administration lawyers] provided will go down in history as some of the most irresponsible and shortsighted legal analysis ever provided to our nation’s military and intelligence communities,” Senator Graham, a Republican of South Carolina and an Air Force Reserve colonel who teaches military law for the service, said.

The hearing is the Senate Armed Services Committee’s first look at the origins of harsh interrogation methods and how policy decisions were vetted across the Defense Department. Its review fits into a broader picture of the government’s handling of detainees, which includes FBI and CIA interrogations in secret prisons.

The panel is expected to hold further hearings on the matter and release a final report by the end of the year.

Among its initial findings is that senior Pentagon lawyers, including the office of general counsel William “Jim” Haynes, sought information as early as July 2002 regarding a military program that trained American troops how to survive enemy interrogations and deny foes valuable intelligence.

Much of the training program, known as “Survival, Evasion, Resistance and Escape,” is based on experiences of American prisoners of war in previous conflicts, including those in Korea and Vietnam.

In response, SERE officials provided Mr. Haynes’s office a list of tactics that included sensory deprivation, sleep disruption, and stress positions.

Mr. Haynes, who resigned his post in February, testified that he remembers receiving the information, but that he did not recall requesting it personally.

Several of those techniques, including stress positions, were later approved by Defense Secretary Rumsfeld in a December 2002 memo for use at Guantanamo Bay. Messrs. Rumsfeld and Haynes agreed to the methods, despite objections by military service lawyers that they might be illegal.

“Whatever interrogation techniques we adopt will eventually become public knowledge,” wrote Colonel John Ley of the Army’s Judge Advocate General office in November 2002. “If we mistreat detainees, we will quickly lose the [moral] high ground and public support will erode.”