BAGHDAD, Iraq - The highest-ranking soldier charged in the Abu Ghraib scandal pleaded guilty today to five charges of abusing Iraqi detainees at the prison as a two-day court-martial opened at a U.S. base in Baghdad.

U.S. Army reservist Staff Sgt. Ivan "Chip" Frederick, 38, of Buckingham, Va., admitted to allegations of conspiracy, dereliction of duty, maltreatment of detainees, assault, and committing an indecent act. He was expected to be sentenced Thursday.

Under a plea bargain deal, several other charges against Frederick - a military policeman and a corrections officer in civilian life - were dropped, according to his attorney, Gary Myers.

The Abu Ghraib prisoner scandal broke in April with the worldwide publication of photos and videos showing American soldiers abusing and humiliating naked Iraqi detainees.

Frederick is alleged to have watched as a group of detainees were made to masturbate while other soldiers photographed them. He also is accused of jumping on a pile of detainees, stomping on detainees' hands and bare feet, and punching one in the chest so hard he needed medical attention.

In addition, Frederick allegedly helped place wires in a detainees' hands and told him he would be electrocuted if he fell off a box.

Frederick is one of seven members of the Cresaptown, Md.-based 372nd Military Police Company charged in the scandal.

Frederick, who was in charge of the night shift at the "hard site" facility at Abu Ghraib, told military judge Army Col. James Pohl that Military Intelligence and civilian interrogators "would tell us what conditions to set for (detainees)."

That included removing detainees' clothing, depriving them of sleep, or taking away their cigarettes, Frederick said. He said they wanted detainees "stressed out, wanted them to talk more."

During a notorious Nov. 4 incident captured on camera and transmitted around the world, Frederick said he had helped place wires on a detainee's hands and told him he would be electrocuted if he fell off a box.

"I took one and wrapped it around his finger. Sgt. (Javal) Davis put one on his hand. Spc. (Sabrina) Harman one on his toe," he said.

Frederick said he thought the interrogator wanted him to scare the prisoner to help out with the interrogation.

"Did you think what you were doing was right?" the judge asked.

"I was wrong about what I did and I shouldn't have done it. I knew it was wrong at the time because I knew it was a form of abuse," Frederick replied.