A Gaithersburg teen-ager has filed a $25 million lawsuit against Montgomery County and its corrections officials, accusing them of failing to protect him from rape while he was a prisoner at the county detention center earlier this year.

Robert Bruce Mostoller, who was awaiting trial on a charge of auto theft, said he was placed in an area of the jail on Feb. 26 with Jerry Lee Polite, 21, of Washington, who according to the court papers was a known sex offender.

Mostoller, who was 18 at the time, was described in the lawsuit filed last week in Montgomery County Circuit Court as "slightly built." He said that "without forewarning and certainly without his consent" he was "violently raped" by Polite, who was described as "a physically powerful" 200-pounder.

As a result of the attack on Mostoller, Polite was charged with and convicted of sodomy, according to court papers. At the time, Polite was awaiting trial on an armed robbery charge that was subsequently dismissed. He currently is serving time in the District, acccording to Samuel F. Saxton, deputy director of the Montgomery County Detention Center. Polite will be returned to Maryland upon his release to serve time on the sodomy conviction, Saxton said.

Mostoller was convicted of the auto theft and placed on probation, Saxton said.

Last month, a Montgomery County grand jury indicted four other inmates on charges of sexually assaulting a mentally retarded inmate who was being held overnight at the detention center in Rockville.

In Prince George's County, a special grand jury is investigating sexual attacks in the jail at Upper Marlboro that were the subject of a series of articles in The Washington Post.

Mostoller's lawsuit names as defendants the Montgomery County government and three corrections officials, director Gary B. Blake; deputy director Saxton, and Charles Hessling, director of custody and security.

"It was known to Montgomery County jail officials and the defendants that inmate Polite had on previous occasions sexually attacked other persons . . . . " Mostoller claimed in court papers. "The plaintiff was not warned by defendants as to the propensity of inmate Polite to commit homosexual rape, although such fact was known or should have been known to the defendants."

"There are still a lot of questions as to what really happened in that incident," said Saxton, who acknowledged that Mostoller had previously been involved in a sexual attack on another prisoner. "The alleged assault on Mostoller occurred at the time we had a serious fire here in the institution. Both Mosteller and Polite were on Level 6-C1, although not assigned to the same cell."

"The rest of the inmates were out watching the fire trucks. It [the fire] was a life-and-death situation," Saxton said. "Two hours after the alleged assault, Mustoller approached an officer making his rounds and reported that he had been sexually assaulted."

Saxton said there was no evidence that Mostoller was forced to enter Polite's cell. An examination of Mostoller by doctors showed no signs of rape, according to Saxton.

"The defendants were under a duty to separate known sex offenders from the general population," Mostoller wrote in the suit, "especially those portions of the prison population who might be deemed to be a target or particularly susceptible to being victimized sexually by other inmates."