Three male former inmates of the Prince George's County Detention Center, charged with first degree sex offenses in the alleged rape of a fellow male prisoner, pleaded guilty yesterday to lesser charges of assault and battery in the case. Circuit Judge Jacob S. Levin sentenced each to one year in prison to run concurrent to sentences they are already serving.

The case of a fourth inmate, charged similarly in the same incident, was postponed until Aug. 1.

According to prosecutors' allegations, Otis Thomas Praylow, 22, Joseph Del Mundo, 29, Kevin Frank Wilson, 21, and Joseph Leon Smith, 22, sexually assaulted a 21-year-old College Park man in the county jail in Upper Marlboro on March 18, 1980. Assistant State's Attorney Robert Harvey said they "grabbed" the man, "fought with him, and forced him to submit to anal intercourse."

Praylow, from Northwest Washington, is serving a five-year sentence for attempted break and entry. Mundo, also from the District, is serving a 15-year-sentence for armed robbery. Wilson, of Brentwood, is serving a seven-year sentence for assault with intent to maim and armed robbery. All are currently in state prisons. Harvey said today's guilty pleas will likely delay parole for the three.

Smith is being held in the county jail awaiting the sexual assault trial. He was being held on a trespassing charge at the time of the incident and was later convicted of that charge. He has pleaded not guilty to the sexual assault charges.

Prosecutor Harvey said the sexual assault was reported to jail officials at the time, and the victim was taken to the sexual assault center at Prince George's General Hospital. Doctors found evidence of an assault but no physical damage, Harvey said.

The victim, Gerald Mohler, described the incident in a series on rapes and sexual assaults in the county jail published in The Post last September. Mohler, who was awaiting trial on armed robbery charges for which he was later convicted, said he was subjected to harassment after the gang rape, and subsequently agreed to provide sexual favors to another inmate in return for protection.

In February, the American Civil Liberties Union filed a $425,000 damage suit against Prince George's County on behalf of Mohler. The suit, filed in U.S. District Court in Baltimore, alleges that jail workers and county officials acted with negligence and/or deliberate indifference to the personal safety of Mohler, in violation of his constitutional rights. The suit is pending.

After the series was published, 12 current or former inmates of the jail, including the four charged in the Mohler case, were indicted by a special grand jury on counts of sexual assault and attempted sexual assault.

One of those inmates, Ronald P. Garnett, 24, was convicted by a jury of assault and battery. The jury failed to reach a verdict on sexual assault charges, and so far, no new trial has been scheduled. Trials for the remaining seven inmates are scheduled for later this year, and the special grand jury is continuing its investigation.