Five more men were indicted yesterday by a special grand jury investigating rapes and sexual assaults among male inmates in the Prince George's County Detention Center in Upper Marlboro.

The indictments charged that the men forced, or attempted to force, fellow prisoners in the jail to have sex with them. The same grand jury handed down similar indictments two weeks ago against seven men. One of those seven was indicted yesterday on charges arising from a separate incident, along with the five.

Yesterday's action brings to 12 the number of alleged offenders indicted since the grand jury was impaneled in October following a Washington Post series on rapes and sexual assaults in the jail. Inmates and guards said in the series that about a dozen sexual attacks occurred a week at the jail.

Among those indicted yesterday were Timothy Earl Lipscomb, 21, of Seat Pleasant, and Clifton Earl Tucker Jr., 19, of Northeast Washington. Tucker is the man indicted on similar charges two weeks ago.

Yesterday's indictments against Lipscomb and Tucker stem from an alleged assault last February on Kevin Parrish, a 20-year-old art student from Upper Marlboro, assistant State's Attorney Robert C. Bonsib said yesterday. In the incident, as described in the Post series by participants, Parrish, arrested on drunk-driving charges, was assaulted less than an hour after he was put in jail and several hours before his mother bailed him out with $50. According to Parrish, his two attackers beat him and ordered him to perform oral sex.

At the time, Lipscomb was waiting trial on an armed robbery charge and Tucker, a convicted armed robber, was in the county jail awaiting reconsideration of his sentence.

Parrish said he managed to escape his attackers, and was treated by the jail medic. He identified his assailants from photos, but decided not to bring charges, he said, after a guard told him "there's always the possibility they'll retaliate against you."

Yesterday's indictments against Lipscomb and Tucker included charges of attempting to commit a first-degree sex offense and assault and battery. A first-degree offense occurs when one or more persons help another person assault someone sexually.

Tucker was convicted of armed robbery and is currently in the Maryland Correctional Institution in Hagerstown. Lipscomb, still waiting trial, was released on personal recognizance on Feb. 26, six days after the alleged assault on Parrish.

Parrish was not available for comment last night. But his mother, who asked not to be named, said that her son "should never have been thrown in a place like that with all those type of people." Her son was found guilty of driving while intoxicated, she said, and was put on probation for one year.

Yesterday's indictments of four other men stemmed from the alleged gang-rape on March 18, 1980, of Gerald M. Mohler, a 21-year-old from College Park.

Otis T. Praylow, 22, Joseph Del Mundo, 29, Kevin Frank Wilson, 21, and Joseph Leon Smith, were each indicted on charges including first- and second-degree sex offense.

Mohler told The Post he remained in a locked cell for several days after the gang-rape, but eventually asked guards to let him out. He then joined about 40 other inmates, he said, some of whom threatened him with rape. Mohler said he asked a jail guard to move him to a safer section, but was told he had to "deal with" the harassment because he was already in the safest section, according to Mohler and another inmate.

Mohler, who was convicted of armed robbery, said he then allowed another inmate to protect him from harassment and rape in exchange for sexual favors.

Praylow, of 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. Joseph Leon Smith began serving an 18-month sentence for theft and trespassing last April, but is now in Lorton Reformatory.

Bonsib said the grand jury is continuing its investigation.