WASHINGTON — Interrogators at the U.S. detention facility at Guantánamo Bay, Cuba, forced a suspected terrorist to wear women's underwear on his head, confronted him with snarling dogs and attached a leash to his chains, according to a newly released military investigation that shows the tactics were employed there months before military police used them on detainees at the Abu Ghraib prison in Iraq.

The techniques were approved by Defense Secretary Donald Rumsfeld for use in interrogating Mohamed al-Qahtani — the alleged "20th hijacker" in the Sept. 11 attacks — at Guantánamo Bay in late 2002 as part of a special interrogation plan aimed at breaking down the stubborn detainee.

According to investigators, the interrogators told al-Qahtani that his mother and sisters were whores, forced him to wear a bra, forced him to wear a thong on his head, told him he was homosexual and said that other prisoners knew it.

They also forced him to dance with a male interrogator and subjected him to strip searches with no security value, forced him to stand naked in front of women and forced him onto a leash, to act like a dog.

Military investigators who briefed the Senate Armed Services panel yesterday called the tactics "aggressive" but said they did not cross the line into torture, which involves inflicting physical pain or withholding food, water or medical care.

The report's findings are the strongest indication yet that the tactics seen in photos at Abu Ghraib were not the invention of a small group of military police at the prison.

The report shows that they were used on al-Qahtani several months before the United States invaded Iraq.

A central figure in the investigation, Maj. Gen. Geoffrey Miller, who commanded the detention facility at Guantánamo Bay and later helped set up U.S. operations at Abu Ghraib, was accused of failing to properly supervise al-Qahtani's interrogation plan, and investigators recommended that he be reprimanded. However, Gen. Bantz Craddock, head of U.S. Southern Command, declined to follow the recommendation.

The Guantánamo investigation looked into 26 allegations by FBI personnel that military interrogators had mistreated detainees. It found that almost all the tactics were "authorized" interrogation methods.

Investigators found only three instances of substantiated abuse, including short-shackling detainees to the floor in awkward positions, the use of duct tape to keep a detainee quiet, and a threat by military interrogators to kill a detainee and his family.

In the case of al-Qahtani, who endured weeks of sleep deprivation and many of the harshest tactics, investigators Lt. Gen. Mark Schmidt and Brig. Gen. John Furlow found the cumulative effect of those tactics "resulted in degrading and abusive treatment" but stopped short of torture. Military commanders have said the techniques prompted al-Qahtani to talk.

The military achieved "solid intelligence gains," by interrogating al-Qahtani, Craddock said yesterday, and other military officials have said he revealed details on how the terrorist network operates.