WASHINGTON — Defense Secretary Donald H. Rumsfeld defended military interrogation techniques in Iraq on Wednesday, rejecting complaints that they violate international rules and may endanger Americans taken prisoner.

Rumsfeld told a Senate committee that Pentagon lawyers had approved methods such as sleep deprivation and dietary changes as well as rules permitting prisoners to be made to assume stress positions.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, also noted that the rules require prisoners to be treated humanely at all times.

But Sen. Richard Durbin, D-Ill. said some of the approved techniques "go far beyond the Geneva Convention," a reference to international rules governing the treatment of prisoners of war.

Rumsfeld spoke after two weeks of controversy provoked by photographs of American military personnel abusing prisoners in Iraq. An American was beheaded in a videotaped execution posted to a militant Islamic web site on Tuesday — a killing that captors said was revenge for the abuse of Iraqis in the Abu Ghraib prison.

The Defense Department is conducting multiple investigations into the abuse, and congressional hearings are under way, as well. At the insistence of lawmakers, the Pentagon arranged for members of Congress to view photos and videos during the day. They depict the abuse, including examples of prisoners forced into sexually humiliating poses.