School vandalism ranging from an end-of-the-season egg-throwing melee to the destruction of classroom property worth nearly $10,000 struck two Northern Virginia schools yesterday, officials said.

Prince William County police said vandals at Minnieville Elementary scattered food, flooded 11 classrooms, shattered windows and sacked the teacher's lounge in an early-morning rampage that forced officials to shut the school for the day.

Arlington police later had to send 15 patrol cars to quash egg throwing at Washington and Lee High School. When the officers appeared, about 100 students dashed out of the school and began pelting the squad cars, before the incident ended.

"Springtime is the worst time of the year" for school vandalism, said Ray McGuire, management engineer for the Fairfax school system. "It's when they get active, and the snow melts so that they can find the rocks again."

Both Northern Virginia incidents came a day after Montgomery County police reported a rash of graduation-eve pranks at eight high schools there. At Blair High School 21 students were hospitalized after a World War II tear gas bomb exploded in a second-floor corridor.

Whether motivated by anger at teachers and schools, or the frivolities of "spring fever," vandalism costs Washington area school systems hundreds of thousands of dollars each year.

In Prince William where vandalism can cost upwards of $50,000 a year, Ralph Griffith called the damage to Minnieville school in Dale City "the largest incident of vandalism this year. It's a major mess."

Damage to the Arlington school involved in the egg-tossing incident was said to have been minimal.

Police in Fairfax and Prince William counties said that the majority of the incidents involve juveniles between the ages of seven and 15 who frequently "gear up" for vandalism by drinking beer or wine.

"They usually occur at night between 10 p.m. and 2 a.m. and apprehensions are difficult and closure rates for these cases are frequently low," said Fairfax County police spokesman Warren Carmichael.

"We're talking about typical suburban youngsters that come from well educated, and well-to-do families." Carmichael said. "It's a very big problem."

Many security officials complain that they lack the manpower to adequately guard schools, and that penalties for offenders usually are minimal, if they are penalized at all.