FORT CAMPBELL, Ky. — One of four American soldiers accused of raping a 14-year-old Iraqi girl last spring and killing her and her family pleaded guilty yesterday, agreeing to testify against the others.

Specialist James Barker agreed to the plea deal to avoid the death penalty, his civilian attorney, David Sheldon, said.

The military judge presiding over the case, Lieutenant Colonel Richard Anderson, asked Barker why he participated in the attack in Mahmoudiya, a village about 20 miles south of Baghdad. It was among the worst in a series of alleged attacks on civilians and other abuses by military personnel in Iraq.

“I hated Iraqis, your honor,” Barker answered. “They can smile at you, then shoot you in your face without even thinking about it.”

Colonel Anderson accepted the plea agreement, which calls for Barker to serve at least life in prison. The judge will decide in a hearing today whether Barker should be allowed to seek parole.

Sergeant Paul Cortez, 24, and Private First Class Jesse Spielman, 22, members of the 101st Airborne Division with Barker, also are charged in the case. Sergeant Cortez deferred entering a plea during his arraignment yesterday morning. Private Spielman will be arraigned in December. The fourth soldier, Private First Class Bryan Howard, 19, also deferred entering a plea at his arraignment in October.

A fifth person, a former Army private, Steve Green, 21, pleaded not guilty last week to civilian charges including murder and sexual assault.

Mr. Green was discharged from the Army for a “personality disorder” before the allegations became known, and prosecutors have yet to say if they will pursue the death penalty against him. The group is accused of raping the girl and burning her body to conceal their crimes, then killing the girl’s father, mother, and 6- year-old sister.

After entering his plea yesterday, Barker gave the court a vivid account of the events.

Barker said he and the others were drinking and playing cards while they manned a traffic checkpoint. Mr. Green brought up the idea of raping the girl and killing her family, he said.

“He brought it up to me and asked me what I thought about it. At a couple of points, I told him he was crazy,” Barker said.

Barker said he and Mr. Green then approached the others with the idea, but there never was a verbal agreement to do it.

“Things just got set in motion, we just started changing” clothes, “myself, Cortez, and Green,” Barker said. “By the time we started changing clothes, it was more or less a nonverbal agreement that we were going to go along with what we were discussing.”

Barker said he, Mr. Green and Sergeant Cortez raped the girl, and Mr. Green killed the girl, her parents, and her sister.

Barker did not name Privates Spielman and Howard as participants in the rape and slayings, though he said they were at the house when the assault occurred and had come knowing what the others intended to do.

Sergeant Cortez, who could face the death penalty if convicted, and Private Howard watched from the audience as Barker described the assault. They were accompanied by their defense attorneys and declined to comment.