More than 100 antinuclear protesters who marched on the Virginia Electric Power Co.'s North Anna power plant near here last month were convicted of trespassing today and fined $50 each by a judge who said he believed they acted for moral reasons.

All but 10 of the 109 convicted demonstrators, most of them from Northern Virginia, said they planned to pay their fines or appeal the guilty verdicts. The remaining 10 were taken immediately to the Louisa County jail to begin serving 30-day jail terms imposed by the judge. With time off for good behavior and time already served, the terms could be cut to as little as 18 days.

General District Court Judge William Cooke said he believes the protesters "reasonably thought in their hearts they were doing the right thing." He told the protesters he would not "rule as stern" as Louisa County Commonwealth's Attorney Stephen Harris had requested but would not condone breaking the law.

Harris had asked Cooke to sentence each of the Vepco protesters to 60 days in jail and a $500 fine with the option of suspending the jail term and all but $50 of the fine. The judge chose instead to formally impose 30-day jail sentences and $100 fines, suspending all but a $50 fine on the condition that the demonstrators remain on good behavior for a year.

In a day-long trial that was among the most unusual in the history of this central Virginia county 85 miles southwest of Washington, nearly 200 protestors, their supporters and numerous lawyers packed a tiny, sweltering, fly-infested courtroom.

Spectators and defendants filled the chairs, stood lining the walls, sat on the floor and on window sills and even peeked in through open windows. At one point, a horrified court clerk hastily ejected one woman, who had started to breast-feed her baby while sitting at the defense table in the front of the courtroom.

Seven demonstrators were the first of three separate groups - each with separate sets of attorneys - to come before Cooke. They raised what they called the "necessity defense," arguing that they had no choice but to try to halt the operation of nuclear power plants.

Sebastian Graber, an Alexandria attorney, compared demonstrating against nuclear power with "taking a pregnant woman or a sick child to the hospital. It's justifiable to speed. You may get arrested, but at trial Virginia has recognized there is a greater law requiring concern for human life."

Invoking the name of patriot Patrick Henry, who was born in nearby Hanover County, Graber said it is a Virginia tradition to protect human rights and human life.

"The fact that radiation is invisible and odorless and that you can't feel the radiation coming into this room right now because of North Anna does not lessen the danger," Graber argued.

Judge Cooke refused to allow any expert testimony on the dangers of nuclear power, saying he was unwilling "to make this court a forum on the issue of whether North Anna is safe or unsafe." He said that "only time will tell who's going to be proven right."

"I recognize that nuclear power may be a danger, but a lot of people don't recognize that," said Cooke.

"The court will take into consideration the reasons for doing it in deciding punishment, but the defendants didn't have the right to take the law into their own hand."

James Sprinkle, 33, one of the few protesters who took the stand in his defense, said he had grown up in Virginia and moved back to Madison County, Va., from Colorado after a friend was hurt in a radiation accident in that state.

"I grew up in the '50s and spent many hours in school halls and basements with my head tucked between my knees," during civil defense tests, said Sprinkle, the father of two. He accused Vepco of construction mistakes, mismanagement and lying to the public.

After Cooke sentenced the first group, most of the others pleaded innocent and also adopted a "necessity" defense. They have 10 days to appeal for a jury trial.

The ten who went to jail said they were morally opposed to paying the fine and asked instead if they could spend 30 days or longer working on a community service project. Cooke denied this request.

Some of those headed to jail said late today they plan to continue the protest by staging a hunger strike.

In all, 113 demonstrators were arrested at the Vepco site June 3. In addition to those convicted today, one was tried and convicted last month, another was acquitted because of inadequate arrest warning and two juveniles face trial Thursday.