An inmate at the Montgomery County Detention Center was arraigned yesterday on charges that he and three other inmates sexually assaulted a 27-year-old mentally retarded prisoner who had been arrested on a drunk driving charge and was held overnight in the jail because he could not post a $200 bond.

The accusations of sexual assaults in Montgomery come as a grand jury in neighboring Prince George's County is investigating 12 reports of rapes of inmates there.

The Montgomery County jail, on Seven Locks Road in Rockville, while overcrowded, is considered by penal experts to be a model institution where violence among inmates has been relatively limited in recent years.

According to Capt. Charles Hessling, director of custody and security at the Rockville institution, about eight sexual attacks at the center have been reported and prosecuted in the nine years he has been employed there.

"This facility was designed for 272 inmates and we currently house 430 individuals," Hessling said. "There is a lot of tension and frustration that builds up in the inmates from overcrowding. But there is absolutely no correlation between overcrowding and sexual assaults."

The four inmates, Kenneth D. Walker, 20; Bernard D. Young, 20; Milton C. Moore, 25, and John T. Washington, 24, were indicted last week after two other prisoners who said they witnessed the attack reported it to jail officials.

The four were indicted on one count each of a first degree, second degree and third degree sexual offense. In addition, they were all indicted on charges of unnatural and perverted sexual practice and battery. Washington was arraigned before Judge Leonard Ruben in Montgomery County District Court. Walker, Young, and Moore are scheduled to face arraignment next Friday.

All four men are being held at the detention center without bond.

At the time of the assault, three of the alleged attackers -- Young, Moore and Washington -- were awaiting trial on sex offenses and Washington also was serving time for rape. Walker was awaiting trial on charges of storehouse breaking and assault with intent to rob.

The victim of the attack, who is described in court papers as being "mentally handicapped," was admitted to Lutheran Hospital in Baltimore for treatment after he was released from the jail. The alleged attack lasted eight hours, from 5:30 p.m. on Aug. 23 to 1:30 a.m. on Aug. 24, and was interrupted briefly only once by a passing guard, according to court files.

Dr. A.N. Nagaraju, a psychiatrist who has been treating the victim's disorder since the early 1970s, said his patient was not taking medication and was "insane" at the time of the incident, according to court records.

According to court papers, the victim of the attack had been placed overnight in a holding cell with other inmates after he was arrested by a county police officer and charged with drunk driving. The man had remained in jail because he could not make the bond set by a court commissioner.

In an effort to promote "more harmony" among the inmates and possibly reduce assaults, Hessling said the jail tries to strike a balance between the number of aggressive and the number of passive inmates who are placed in the same cell.

But he said there are no special provisions made at the detention center for persons suffering from mental disabilities. "Ideally, those kinds of people would be sent to some other kind of institution, not the county detention center," he said.

According to court records, the assault of the mentally retarded man began when Moore, Walker, Washington and Young began to "push him around" at 5:30 p.m. on Aug. 23.

During the eight-hour ordeal, according to court papers, each man took his turn punching and beating the man and forcing him to perform oral sex acts as other inmates in the cell looked on.

At one point, Walker stopped his alleged sexual assault of the man while a guard passed by, according to court records. Then, the assault continued.

The Prince George's grand jury investigation was called by State's Attorney Arthur A. Marshall Jr. after a series of stories in The Washington Post described a number of sexual assaults at the jail.

The newspaper named and quoted prisoners who admitted the rapes, but a source close to the investigation said the rapists could not be indicted simply on the words of the victims.

But defense lawyer Darlene Perry said grand juries frequently indict men for rape on the word of the female victims. And last year, a Hyattsville woman was indicted on the word of an 8-year-old boy who claimed that she had raped him. There was no medical evidence for the rape and the woman was later acquitted.