A 23-year-old Gaithersburg man was convicted yesterday of raping and committing other sexual offenses on a 13-year-old girl last March after she was abducted outside a wedding reception she had attended in Rockville.

The man, John Norris Anderson, is the first of five defendants in the case to stand trial. He could be sentenced to life in prison on each of three of the convictions: for first degree rape, first degree sex offense and first degree attempted rape. He could receive another 20 years for second degree rape and 10 for a third-degree sex offense.

The convictions were returned by a Montgomery County Circuit Court jury after about an hour and 20 minutes of deliberation. Sentencing was scheduled for Sept. 4.

The prosecution dominated the four-day trial by presenting witness after witness, including one alleged accomplice, to piece together the girl's hour-long ordeal. According to testimony, she was taken from a parking area near the church to Gaithersburg, where she was raped in an apartment, and then to a field off Snouffers School Road where she was raped again.

Defense attorney William Haugh, who offerred no witnesses, told the jury in his closing statement there was no direct evidence that Anderson had been involved. "The victim herself doesn't remember a thing," Haugh declared, despite the repeated use of hypnosis to stimulate her memory.

Noting that Anderson, who lived at 1 Summit Dr., Gaithersburg, was arrested the morning after the incident hiding in a closet of an apartment occupied by his girlfriend, Haugh said, "It's not as difficult to find voluntary sexual partners as it was 10 years ago. Why take the risk of long prison term?"

The incident began at 11:30 p.m. on March 17, the girl testified, when she was standing by the curb and a car stopped, apparently to ask directions. "I turned around and they pulled me into the car . . . on the floor of the back seat. I went blank . . ." She testified she no longer remembers being raped.

Robert Parks, 21, who said he drove the car, testified that the girl repeatedly vomited while being attacked. Parks said he drove to the woods, rolled up the window and turned up the car radio so he wouldn't hear the girl's screams while the other four men raped her. Parks is charged with rape.

Michael Limparis, who lives near the field, testified that he and his fiancee heard the girl's screams and drove to investigate and the five men fled. Limparis said that when he went to the girl's aid, she said, "I'm only 13 and I've just been raped."

Limparis copied the car's license number, he said, enabling police to trace the suspects. Laboratory tests on Anderson's underwear, a statement a jail inmate testified Anderson made to him, and Parks' testimony all linked Anderson to the rape.