The sentences mark the latest development in a tumultuous period for the 1st Battalion of the National Guard's 184th Infantry Regiment.
The battalion has been the subject of a wide-ranging investigation into allegations of misconduct over the last year. In the last month, it has been involved in a spate of violent encounters with insurgents and suicide bombers, leaving four soldiers dead. Overall this year the battalion has had 71 combat-related injuries and seven soldiers killed in action, meaning that about 10% of its soldiers have been wounded or killed.
Lt. Col. Robert L. Whetstone, spokesman for the 3rd Infantry Division in Iraq, said Friday that three sergeants from a Fullerton-based company of the battalion have been confined to military prisons for their role in the abuse of detainees.
All pleaded guilty at special courts-martial and were sentenced by a military judge to terms of up to 12 months of confinement, as well as reduction in rank and forfeiture of pay.
The military has declined to discuss the allegations against the soldiers in detail. But the accusations appear to focus largely on abuse that took place in March at a power plant near Baghdad.
An unknown number of Iraqis were taken into custody there, military officials have said, and were tortured or otherwise mistreated by soldiers.
The Iraqis were believed to be insurgents at the time they were taken into custody, but one member of the battalion, speaking on condition of anonymity because he is not authorized to talk about the incident, said none were insurgents, though several appear to have been common thieves. All but one of the detainees were soon released.
The abuse involved the use of a stun gun on men who were handcuffed. The stun gun was used on at least one man's testicles, the member of the battalion said.
A portion of the abuse was captured on video. A soldier who was not involved in the mistreatment later discovered the footage on a laptop computer and gave it to his commanders.
Other members of the battalion have sought in recent months to downplay the incidents, saying the abuse was led by Iraqi soldiers and was merely witnessed by U.S. soldiers who were patrolling with them.
But Whetstone placed the blame on the American soldiers, saying that although some of them were accused of "failing to stop the abuse of others," none of the abuse "coincided with abuse by Iraqi soldiers."
"Iraqi police were present for one incident of abuse, but there is no evidence that their actions were inappropriate or abusive," Whetstone wrote in an e-mail from Iraq.
The stun-gun incidents are one focus of a broad investigation into possible wrongdoing in the battalion.
Among the accusations that investigators have examined are complaints that soldiers from the battalion charged unauthorized "rent" to Iraqi-owned businesses operating on an Army base.
A first sergeant was also relieved of duty after he was accused of feigning an Iraqi's execution by firing his pistol next to the detainee's temple.
The battalion's commander, Lt. Col. Patrick Frey of Salinas, was suspended from duty. Military officials say he has since been replaced by an active-duty Army officer and reassigned. His current location and assignment are unknown.
Last year, soldiers in the battalion caused a stir by going public with concerns that their training for Iraq was so poor that they would suffer needlessly heavy casualties.
Today, with seven combat deaths, the battalion, headquartered in Modesto, has recorded the most soldiers killed in action of any California unit in Iraq.