A jury acquitted a Montgomery County policeman yesterday of raping a 15-year-old girl in the basement of a Bethesda elementary school in February.

The verdict in Montgomery County Circuit Court followed two hours and 40 minutes of deliberation. The officer, 33-year-old Joseph Baltimore of the Bethesda police station, testified earlier in the day that he never had sexual relations with the girl and denied touching her when the attack was alleged to have occurred - early Feb. 13 in a basement room of the Brookmont Elementary School.

The verdict was greeted with applause from courtroom spectators, many of whom were police officers.

Baltimore said he plans to return to the force, from which he had been suspended, but that he plans to seek another job because police work has "too much pressure." Earlier he said he felt he had been treated unfairly by the police department because he was suspended without pay.

Baltimore's attorney, Courtland K. Townsend, called his client the "best witness" in the trial.

In his testimony yesterday, Baltimore said he met the 15-year-old and her 14-year-old friend for the first time a day before the alleged rape when another policeman told him to take them home because they were both "pretty intoxicated."

He agreed to meet them again, he testified, because he was told they urgently wanted to see him.

Townsend said earlier in the trial that the 15-year-old was known to police as an informer.

When he met them early on Feb. 13, Baltimore said, both girls "had the odor of alcohol and their eyes were bloodshot." He said he sat in the front seat of another officer's police cruiser reading classified ads while they sat in the back seat.

Then, when asked by the other officer to take the girls home again, Baltimore said, both got into his cruiser, the 14-year-old falling asleep in the back seat and the 15-year-old sitting in front and putting on Baltimore's police hat.

The 15-year-old offered to show him an area in the basement of the Brookmont Elementary School, 4300 Sangamore Rd., called the "partying room," where she said youngsters gathered to smoke marijuana and drink beer.

Leaving the 14-year-old sleeping in the cruiser, Baltimore testified, he and the 15-year-old went to the school and climbed through three holes to gain entry to the basement and the "partying room."

The room's dirt floor was strewn with beer cans, wax drippings and cushions, Baltimore testified.

"I thought perhaps I had hit the jackpot," he said, but he "felt under pressure" to return quickly to his unattended cruiser. He said he and the girl were in the room only about a minute.

The 15-year-old testified last week that Baltimore raped her in the room.

Baltimore testified yesterday he didn't touch the 15-year-old and that when he later dropped both girls off, the 15-year-old was "talkative and happy" but expressed concern that he would tell others that she had showed him the "partying room."

She said, "I know you're cool, you won't tell . . .' She told me she had . . . brothers and I was her brother also . . . I said nothing." Baltimore testified.

In closing arguments, Deputy State's Attorney Timothy E. Clarke portrayed Baltimore as an officer who had "betrayed the trust placed in him." He asked for a first degree rape verdict, which carries up to life imprisonment, and cited physical evidence, including pubic hair found on the girl's body that "matched up" with Baltimore's pubic hair, and semen found on both the girl's and Baltimore's underwent.

Defense Attorney Townsend called the pubic hair evidence inconclusive since experts were unable to identify any "Negro characteristics" in the hair specimens offered as evidence. Baltimore is black. Townsend also suggested that the semen found on the girl's underwear was not Baltimore's since "we don't know her (the girl's) actual whereabout 24 . . . or even before the alleged rape took place.