A Montgomery County Circuit Court jury, after deliberating 11 minutes yesterday, convicted an antiabortion activist of trespassing at a women's health clinic despite her efforts to try to put abortion on trial instead.

Gay Sanseverino, 23, of Damascus, who described her occupation as "mother," requested a jury trial and insisted on defending herself. But Judge Richard Latham denied her motion to use what is known in law as the "necessity defense."

The necessity defense generally holds that harm resulting from the crime is not greater than the harm the defendent is trying to prevent.

Sanseverino, nonetheless, addressed that issue in her closing arguments, saying in effect that she had no choice but to trespass "to save the unborn."

She was arrested and charged with trespassing June 16 after she repeatedly refused to leave the waiting room of the Uptown Women's Clinic in Gaithersburg, where she had gone to distribute literature and try to counsel women.

Although unsuccessful, her defense effort reflects a renewed interest among antiabortionists in the strategy.

The interest has been spurred by recent cases won by antiwar protesters.

On Feb. 14, 1984, the Superior Court of Pennsylvania overturned the burglary conviction of Philip Berrigan and others, saying they should have been allowed to argue that their efforts to thwart nuclear war were less harmful than war.

Last December, a Montpelier, Vt., jury acquitted 26 antiwar protesters of trespassing after they used the necessity defense. They had sat in at Sen. Robert T. Stafford's (R-Vt.) office to protest U.S. policies in Central America.

Steve Settle, spokesman for the Milwaukee-based Catholic League, a 33,000-member nonprofit civil and religious rights organization that opposes abortion, said, "We're finding a great deal of precedent set for us by antiwar protesters. They've done our homework for us. We're going to ride this thing for all it's worth."

In her closing arguments, Sanseverino said, "I was under a compelling state of mind. I admit that I was trespassing, but I had to do it. I didn't have any other choice but to be there -- it's just a natural reaction I have when children, born or unborn, are in danger."

However, Assistant State's Attorney Cynthia Ross told the jury in her closing statement, "You are not here to decide whether or not abortion is good or bad. You are here to decide whether or not Gay Sanseverino is guilty of trespassing."

Sanseverino faces up to three months in jail and a $500 fine. She is scheduled to be sentenced May 2.