A 30-page report by Human Rights Watch describes an Army captain's 17-month effort to gain clear understanding of how U.S. soldiers were supposed to treat detainees, and depicts his frustration with what he saw as widespread abuse that the military's leadership failed to address. The Army officer made clear that he believes low-ranking soldiers have been held responsible for abuse to cover for officers who condoned it.

The report does not identify the two sergeants and a captain who gave the accounts, although Capt. Ian Fishback has presented some of his allegations in a letter to Sen. John McCain (R-Ariz.).

Their statements included vivid allegations of violence against detainees held at Forward Operating Base Mercury, outside Fallujah, shortly before the notorious abuse at the Abu Ghraib prison began. The soldiers described incidents similar to those reported in other parts of Iraq -- such as putting detainees in stress positions, exercising them to the point of total exhaustion, and sleep deprivation.

They also detailed regular attacks that left detainees with broken bones -- including once when a detainee was hit with a metal bat -- and said that detainees were sometimes piled into pyramids, a tactic seen in photographs taken later at Abu Ghraib.

"Some days we would just get bored so we would have everyone sit in a corner and then make them get in a pyramid," an unidentified sergeant who worked at the base from August 2003 to April 2004 told Human Rights Watch. "This was before Abu Ghraib but just like it. We did that for amusement."

And like soldiers accused at Abu Ghraib, these troops said that military intelligence interrogators encouraged their actions, telling them to make sure the detainees did not sleep or were physically exhausted so as to get them to talk.

"They were directed to get intel from them so we had to set the conditions by banging on their cages, crashing them into the cages, kicking them, kicking dirt, yelling," the soldier was quoted as saying. Later he described how he and others beat the detainees. "But you gotta understand, this was the norm. Everyone would just sweep it under the rug."

Army and Pentagon officials yesterday said they are investigating the allegations as criminal cases and said they learned of the incidents just weeks ago when the Fort Bragg captain's concerns surfaced. Paul Boyce, an Army spokesman, said the Army began investigating as soon as it learned of the allegations.

Lt. Col. John Skinner, a Pentagon spokesman, severely criticized the report and emphasized that the military has taken incidents of detainee abuse extremely seriously since the Abu Ghraib scandal, changing policies and procedures to prevent such mistreatment. There have been hundreds of criminal investigations and more than a dozen major inquiries.

"This is another predictable report by an organization trying to advance an agenda through the use of distortions and errors in fact," Skinner said. "It's a shame they refuse to convey how seriously the military has investigated all known credible allegations of detainee abuse and how we've looked at all aspects of detention operations under a microscope. . . . Humane treatment has always been the standard no matter how much certain organizations want people to believe otherwise."

In addition to talking to Human Rights Watch, Fishback has made his concerns known in a series of signed letters and memos sent to Capitol Hill. Fishback, a West Point graduate who has served in Afghanistan and Iraq, wrote that no one in his chain of command has been able to give him a clear explanation of what humane treatment is, and he believes that U.S. soldiers have regularly violated the Geneva Conventions by torturing detainees and taking family members hostage as a means of coercion.

"Despite my efforts, I have been unable to get clear, consistent answers from my leadership about what constitutes lawful and humane treatment of detainees," Fishback wrote in a Sept. 16 letter to McCain, a member of the Armed Services Committee and a former prisoner of war in Vietnam. "I am certain that this confusion contributed to a wide range of abuses including death threats, beatings, broken bones, murder, exposure to elements, extreme forced physical exertion, hostage-taking, stripping, sleep deprivation and degrading treatment." Fishback, reached by telephone yesterday, declined to comment.

Tom Malinowski, Washington advocacy director for Human Rights Watch, said yesterday that the report again shows the need for an independent investigation into detainee abuse, and for Congress to define how U.S. soldiers are to treat detainees in their custody. "Even officers who wanted to behave honorably found it difficult to do so because there was no clarity about what the rules are," Malinowski said.