Four antiabortion demonstrators were given $500 fines and 60-day suspended jail sentences yesterday by a federal judge who sternly told them that their continuing invasions of a Fairfax County abortion are "a tragedy."

District Court Judge J. Calvitt Clarke Jr., his voice rising in a rare display of anger, cut short the demonstrators' explanations of their cause and cautioned them they may be jailed for their actions.

"Some children are going to jail for reasons that I think somebody is keeping them stirred up and it's tragedy; it's a tragedy," the judge said as he found the four guilty of contempt of court for violating a court order that restricts protest at the clinic.

After an emotional three-hour hearing before the Norfolk judge in an Alexandria courtroom, little seemed to have been resolved. Two demonstrators said they probably will not pay the fines and will go to jail over the issue.

Clarke, who earlier this summer laid down specific provicions for protests near the Northern Virginia Women's Medical Center, ordered the jail sentences suspended and placed the four on 90-day probations.

If the demonstrators do not pay the fines within 30 days, they must begin serving the jail sentences, court officials said.

"I'm not hoping to go to jail," said Diane Bodner, 19, a University of Maryland student, after sentencing. ". . . I've heard some bad things about it. But if I don't (act to stop abortions), who will? People will have to do it. We have to keep on doing it over and over again until people change their minds" about abortions.

In the courtroom, the protesters defended themselves on the stand, saying they acted to protect the lives of unborn babies regardless of what a judge might rule.

"I feel very strongly about this issue as you do. I feel sympathy for this issue," Clarke told the protesters after sentencing them, shaking his head. "This has got to stop . . . You people have just got to realize that. you're a nice bunch of kids. you're sincere. It's very painful for me to exact any penalty on you."

Yesterday as antiabortion protesters picketed the courthouse, there was a confrontation between one of the protesters and a federal marshal in Clarke's courtroom. The marshal in pulled a screaming pregnant woman from the chamber after she brushed a marshal's effort to restrain her from touching the defendants.

The court hearing was the latest episode in a prolonged controversy between the medical center, at 3918 Prosperity Ave., and the demonstrators, who are upset over the 16,000 abortions performed at the clinic since it opened in 1973. On June 23 Clarke issued an order, said to be the first of its type in the nation, forbiding the demonstrators from entering the clinic, but allowing them to demonstrate near it.

The four protesters sentenced yesterday went to the clinic July 20 and were arrested by Fairfax County police on trespass charges. They are scheduled to be tried Aug. 18 on those charges.

In addition to Bodner, those sentenced were; Jeanne Marie Miller, 18, of 2905 Barrister La., Bowie, a Yale University student; Mary Beth McKernan, 18, of 10500 Arlington Blvd., Arlington, a Biship Denis J. O'Connel High School graduate, David and Gaetano, 27 of 2509 Urbana Dr., Wheaton, a bookkeeper.

"If necessary, we will go to jail," said Gaetano after the court session. "But we don't want," McKernan said she would pay the fine if she can raise the money and Miller said she was uncertain what she would do.

Clarke, who usually exhibits a great deal of patience, yesterday cut shortly the protesters' and their lawyers' statements on abortions and repeatedly lectured them on the law and their obligation to obey it.

When Gaeton said on the stand that he defied the judge's order "to try to prevent a killing of unborn babies," Clarke said, "Oh, I'm not paying any attention to it (Gaetano's testimony.)" Clarke said the Supreme Court had already decided the abortion issue and the case before him was whether the protesters had violated his order.