HAGERSTOWN, MD. – The court-martial of an Army dog handler charged with abusing detainees at the Abu Ghraib prison in Iraq could help clarify who approved the harsh treatment that human-rights advocates say amounted to torture.

Sergeant Michael Smith, 24, is accused of using his unmuzzled dog to harass, threaten, and assault detainees in late 2003 and early 2004 – the same period in which guards at the prison subjected inmates to sexual humiliation and other abuses documented in widely seen photographs.

Military justice experts and civil rights activists expect Sergeant Smith’s attorneys to argue that his actions, documented in some of those Abu Ghraib photos, were condoned by superiors in a chain of command stretching to the Pentagon.

Prosecutors, however, have portrayed Sergeant Smith and another dog handler, Sergeant Santos Cardona, as rogue military policemen who made a game of trying to frighten prisoners into urinating or defecating on themselves.

Sergeant Smith’s trial was set to begin today at Fort George G. Meade, midway between Baltimore and Washington. He faces up to 29 1/2 years in prison if convicted on all 14 counts. Sergeant Cardona’s trial is set for May 22.

The nine soldiers convicted so far in the Abu Ghraib scandal have all been low-ranking reservists.

“The big problem for me here is they’re nailing these low-level guys,” said Michael Ratner, president of the New York-based Center for Constitutional Rights. “A vigorous defense is that this stuff was authorized from the top.”

Kathleen Duignan, executive director of the National Institute of Military Justice in Alexandria, Va., said the trials could reveal how military dogs were supposed to be used at Abu Ghraib, and how high up the chain of command the approvals went.

Evidence showing a lack of direction from above also could help the defendants, said Ms. Duignan, a former military lawyer with the Coast Guard.

Sergeant Smith, of Fort Lauderdale, Fla., has told investigators that he and Sergeant Cardona used their unmuzzled dogs to help military intelligence interrogators. His dog allegedly bit one inmate on the wrist, but not hard enough to break the skin, according to previous testimony.

An Army report on the abuses at Abu Ghraib quotes Sergeant Smith as saying dogs were supposed to be muzzled during interrogations, but “from what I was told, we weren’t doing interrogations. Having the dogs bark at detainees was psychologically breaking them down for their interrogation purposes.”

Dog teams were sent to Abu Ghraib in November 2003 on the recommendation of Major General Geoffrey Miller, who had supervised the American detention facility at Guantanamo Bay, Cuba, and was later put in charge of Abu Ghraib. General Miller has said he recommended in 2003 that dogs be used for detainee custody and control, but not for interrogations.

His account conflicts with that of Colonel Thomas Pappas, the former top-ranking intelligence officer at Abu Ghraib, who told investigators that General Miller told him dogs had been useful at Guantanamo Bay in setting the atmosphere for interrogations.

An independent panel led by former Defense Secretary James Schlesinger found that Pappas “never understood the intent as described by Major General Miller.”

At a preliminary hearing for Sergeants Smith and Cardona in July, former Abu Ghraib warden Major David DiNenna said he understood General Miller had been sent to Iraq by Defense Secretary Donald Rumsfeld. Major DiNenna also testified that General Miller sent trainers to Iraq “to take these interrogation techniques, other techniques they learned at Guantanamo Bay and try to incorporate them in Iraq.”

Colonel Pappas has been granted immunity from prosecution and been ordered to testify if called in the dog handler trials.

General Miller probably won’t be called since he invoked his right not to incriminate himself.