An Army judge sentenced Spec. Jeremy C. Sivits to one year in prison Wednesday for his role in abusing Iraqis at Abu Ghraib prison, closing out the first prosecution of an American in the scandal. Sivits, who provided a detailed account of the mistreatment he witnessed, tearfully apologized in court to the Iraqi people and the victims, saying: "I let everybody down."

Sivits was sentenced after pleading guilty to four criminal counts and agreeing to testify against six other accused Americans.

About 150 angry Iraqis rallied near the makeshift military courtroom, denouncing as a whitewash the start of a judicial process that U.S. officials have said they hoped would demonstrate their resolve to punish all Americans who committed crimes in the prison and mollify widespread Arab anger.

During a four-hour hearing, Sivits testified that he witnessed repeated acts of violence the night of Nov. 8 when he was summoned to help fellow members of the 372nd Military Police Company receive custody of seven Iraqi inmates.

Sivits, who was a mechanic attached to the company and not a prison guard, told the court that during a 30-minute period, he saw military police officers from the unit stomp on the toes and fingers of a pile of detainees, strip them of their blue and orange jumpsuits and civilian clothes and force them to simulate and perform sexual acts with one another. He said the soldiers also hit two prisoners, one so hard that he blacked out.

Answering a question from the judge, Col. James Pohl, Sivits said he did not know why the soldiers had behaved the way they had. But Sivits said a person present that night told him that members of U.S. military intelligence had encouraged them to "keep doing what they were doing to the inmates because it was working. They were talking." Sivits said he did not believe that was true.

The basics of Sivits's allegations had become public through statements he made to investigators. But his testimony Wednesday presented a lengthy start-to-finish description of behavior in one of the cellblocks where the photos now known around the world were taken.

Three other members of his unit were arraigned Wednesday in the same courtroom before his hearing. Three others have been charged, but their cases have not been referred to courts-martial.

Sivits broke down on the stand repeatedly. "I'd like to apologize to the Iraqi people and to those detainees," he said. "I let everybody down. I should have protected those detainees that night.

"You have to stand up for what's right," he told the court. "You can't let people abuse people like that. It was wrong. It shouldn't have happened."

With members of the news media, some from Arab countries, looking on, Sivits, 24, pleaded guilty to dereliction of duty and three other counts related to failure to stop the abuse and to taking a photograph of the abuse that night.

Sivits begged the judge not to expel him from the Army. Breaking down in tears, the defendant said: "I want to stay in. I love the Army. It's all I wanted to be, an American soldier."

But in sentencing Sivits to a year of confinement, Pohl ordered that he be discharged from the Army for bad conduct and that his rank be reduced to private.

Under a deal with prosecutors, Sivits agreed to testify against six other soldiers in exchange for what is known as a special court-martial, which carries a maximum one-year jail sentence.

Photographs of abuse at the prison have prompted at least five military investigations and congressional probes of the U.S. military's prison and military intelligence operations. Officials have promised to determine how high up the chain of command people were aware of the behavior.

The uproar has created new tensions for U.S. occupation officials preparing to return limited authority to Iraqis at the end of next month.

Outside the courtroom at the Baghdad Convention Center, about 150 people marched up traffic-clogged Shawaf Street at 11 a.m. toward the complex where the court-martial was in session. Shopkeepers and tea vendors watched as the crowd, led by drummers and a horn player, passed waving a series of banners.

"A Public Trial Against Those Who Committed Crimes Against Detainees Is a Just Demand for All Iraqis," read one. Another said: "We Reject Mass Arrests."

Aloft at the head of the column bobbed the now famous picture of Pfc. Lynndie R. England, an Iraqi prisoner at her feet attached to a dog leash in her hand. Under the close watch of U.S. soldiers on rooftops and checkpoints, the protesters demonstrated peacefully in an intersection at the entrance to the convention center for nearly an hour.

"We have to protest against the terrorist ways the Americans use against the prisoners," said Abdul Razzaq Helfi, a poet and member of the Nasserite Socialist Party. "We'll demonstrate until the torture and oppression in the prisons ends."

Bakhtiar Amin, Iraq's new human rights minister, attended Sivits's court-martial with the new president of the Iraqi Governing Council, Ghazi Yawar, Interior Minister Samir Shakir Mahmoud Sumaidy and Dara Noureddine, a prominent Iraqi judge and council member.

Amin said he was pleased that the court-martial was public. "This is a very good sign," he said. "This is an awful crime, and I condemn it firmly. All we asked is these are tried in a fair manner, that the victims . . . are seen as if they were American citizens."

The three other soldiers arraigned Wednesday were Spec. Charles A. Graner Jr., Staff Sgt. Ivan L. Frederick and Sgt. Javal S. Davis. They appeared in court one after the other but declined through their military attorneys to enter pleas. Pohl set pre-trial hearings on June 21 for all three.

England and Specs. Sabrina D. Harman and Megan M. Ambuhl have been charged but have not been referred to a court-martial. Sivits's account alleges wrongdoing by the other defendants except for Ambuhl.

Sivits testified Wednesday that the 372nd had been assigned to Abu Ghraib for about a month when the abuse took place, but up until that time he had had no contact with the prisoners because he was not a guard.

On the night of Nov. 8, he said, the guards were processing seven detainees who had been sent from another part of the prison for allegedly taking part in a riot.

He said he was relaxing in the common area when Frederick asked him to follow him to the prison so they could continue a conversation. It was then that Frederick asked whether he would like to escort one of the detainees to another tier, and he said yes.

As he led the hooded but still clothed detainee by the arm, Sivits said, he rounded a corner and saw a pile of prisoners on the floor. He said England and Davis were stomping on the prisoners' feet and hands.

At some point, Sivits said, a platoon sergeant called down for Davis to stop. "That's enough," the sergeant yelled out. Davis left the room then. Sivits said Harman later wrote "rapeist" on the leg of one of the detainees.

After the prisoners were stripped, Sivits said, England pointed at and made fun of their genitals.

In another incident, Sivits said he saw Frederick strike a detainee in the chest so hard that someone had to get an inhaler to help the man breathe.

Sivits choked up as he recounted how he told the prisoner to watch his chest and imitate his own calm breathing. Sivits said a medic checked the man and said he was fine.

Later, Sivits said, Graner punched a prisoner in the head and complained his wrist hurt. "I told Corporal Graner, I said, 'I think you might have knocked this guy out.' "

Sivits said he watched as the soldiers put the detainees into a pyramid. He acknowledged photographing Graner kneeling on prisoners with his arm cocked back as if about to strike one.

"It was bad enough," he said in court. "They were embarrassed to be in there, what we were doing to them. They didn't see the picture, but they could hear the click and see the flash through the sandbags" that covered their heads.

Sivits said he left when Frederick and Graner forced the prisoners to masturbate. After hearing the account, Yawar and Sumaidy left the courtroom.

"When that started, I had enough and left," Sivits said.

As he was leaving the area, Sivits said, Frederick called out to him: "You didn't see" anything.

Correspondent Scott Wilson and special correspondent Naseer Nouri contributed to this report.

U.S. soldiers secure area around the Baghdad Convention Center, where Sivits's court-martial took place. About 150 Iraqis protested peacefully near the site.Spec. Jeremy C. Sivits pleaded guilty to four criminal counts and agreed to testify against other Americans accused of abusing Iraqi prisoners.