A Prince George's County jury yesterday rejected a 35-year-old federal bookbinder's plea of insanity and found him guilty of trying to murder his former girlfriend, a car saleswoman, last June 8.

Circuit Judge William H. McCullough ordered the defendant, Larry Minster, jailed until sentencing on June 3. He faces up to life in prison.

Minster has been free on bond since shooting Cheryl Dodgson, 27, leaving her permanently paralyzed from the neck down. He revealed no emotion as the verdict was announced. His mother, however, cried loudly as deputy sheriffs snapped handcuffs on her son and led him through the courtroom to the county jail.

According to testimony during the trial, Minster dated Dodgson for several weeks during the winter of 1981-82 and wanted to marry her. When Dodgson said she did not want to see him anymore, he became depressed, according to testimony. Early on June 8 last year he borrowed a motorcycle, drove to the Deerefield Run Apartments in Laurel where Dodgson lived and shot her once in the neck with a handgun as she parked her car, according to testimony.

Several of Minster's friends testified that his personality had changed dramatically in April and May last year as he became depressed and sometimes suicidal.

His condition worsened, they said, after he fell and struck his head at the Bureau of Engraving and Printing, where he worked.

Defense attorney John C. Monahan, supported by defense psychiatrists, called the shooting a "psychotic act." He maintained that Minster, of Howard Avenue in Beltsville, set out to kill himself, and "heard voices" telling him to kill himself in front of Dodgson. But when he saw Dodgson, Monahan said, Minster "tragically" decided to shoot her instead.

Prosecutor Nelson Rupp argued that Minster suffered nothing more serious than a mild concussion from his fall and was perfectly sane when he shot at Dodgson. He called Minster an "immature" and "egocentric" man.

When Dodgson broke off their relationship, he said, "he was rejected and he was upset by that. He chose to commit murder. He had everything, but he didn't have the girl he wanted . . . .

Dodgson's mother, Virginia Johnson, said after the trial that her daughter and the rest of the family were "very pleased" with the verdict.

Dodgson, who has an 8-year-old son from a previous marriage, underwent rehabilitation in a Denver hospital before coming home in March.

Strapped to a wheelchair and attended by a nurse, Dodgson testified briefly during the four-day trial. She is now living with her parents.