Insurance carriers for Fairfax County Schools, in what legal experts say is an unusual tactic against increasing school vandalism, have filed a $6 million suit against three former county high school students who were convicted in 1979 of setting fire to Fort Hunt High School.

The lawsuit against Matthew Musolino III, 20, Timothy M. Greer, 21, and Robert P. Smithwick, 20, was filed in Fairfax County Circuit Court on behalf of the county school board by its four insurance carriers. It asks that the defendants be held liable for "causing extensive damage to Fort Hunt school and personal property therein."

"It's not a frivolous lawsuit," said Michael L. Davis, an Arlington lawyer representing the insurance companies. The fire did $2.7 million in damages. "We don't know exactly what they the three men have financially now but a judgment is good for 20 years and they may inherit some property some day."

The three men are former students at Fort Hunt High School, which is located in southeastern Fairfax County just north of George Washington's estate. They were convicted in 1979 of maliciously burning the school and sentenced to serve one year in jail, perform 3,000 hours of community service and make $10,000 in financial restitution to the county.

None of the three men could be reached for comment but parents for two of the defendants said their sons have paid their penalty for destroying the school and criticized the civil lawsuit.

"I think the suit is totally ridiculous," said Edward F. Smithwick, whose son admitted in court that he threw the gasoline bottle that started the fire and gutted the school. "You can't get blood out of a stone." He said his son is now a college student.

"I'm backing my son all the way," said Matthew Musolino, whose son now works at his father's Hybla Valley gas station. "The kid is just getting started on his own and now this."

Officials of the Fairfax County school system, whose 162 schools last year suffered $408,298 in damage by vandals, said they have no interest in further punishing the three men and that they did not ask the companies to file suit, although the school is listed as the plaintiff in the case.

"Under the contract the insurance company has the right to bring the action," said Thomas Cawley, school board lawyer. "The school board has not endorsed it."

The suit is apparently one of the first growing out of a nationwide concern by both insurance firms and school boards over the rising cost of school vandalism. "Many boards . . . are considering that type of action," said Ivan Gluckman, legal counsel for the National Association of Secondary School Principals in Reston. "There's a feeling that schools ought to at least make an attempt to collect money damages from people causing vandalism."

"I haven't heard of too many cases like that but I would think it might be a better route than taking criminal action against kids since you impress upon them the seriousness of their action without burdening them with a criminal record," said Gwendolyn Gregory, deputy legal counsel for the National School Boards Association in Washington.