Fewer and fewer school buildings in Northern Virginia sit empty during the summer. More and different summer uses of the facilities are being found every year as communities look to the schools as locations for recreation and enrichment activities.

From hatha yoga to Sunday church services, schools are well used when school is out.

To be sure, there are still buildings, particularly elementary schools, that are occupied by little more than a principal and custodial staff during the summer. But principals at many schools in Alexandria and Fairfax and Arlington Counties are busily juggling schedules to fit in a host of different programs.

"Nobody anymore lets a school sit locked up all summer, it's bad business," says Kenneth Buglass, director of facilities for Arlington schools. "You've got a huge capital investment in a school. It's nothing less than stupid to let it just sit."

It's Monday at the Thomas Jefferson Junior High School and Community Center in Arlington. Arlington residents point to the multi-million-dolar facility as a gem among such centers across the nation; it is used more than any other school in the county, according to assistant principal Jack Dent Jr.

Early in the morning, small children begin arriving for a summer day care program. By 9 a.m., the carpeted locker area of the modern school is crawling with kids between kindergarten and junior high age.

The recreation department's game rooms nearby are crowded with older children, mostly boys, who are absorbed in games of ping pong, computer tennis, pool, pinball and chess. In an adjoining room, others are cutting construction paper and fingerpainting. The school's 1 1/2 acre gym is taken over by basketball games and gymnastics.

At night, Thomas Jefferson changes from a raucous center for active kids to a study center. Although frequent disco dances are held and a few recreation programs and gym activities continue, much of the action is in the classrooms.

Adult education classes in English, a Coast Guard safe boating program, distributive education classes in real estate and industrial housekeeping, Univrsity of Virginia extension courses, English as a second language instruction and transactional analysis courses are a few of the offerings at Thomas Jefferson during the summer.

In addition, senior citizens share balanced meals at the center and participate in bridge sessions, square dancing, bingo, classes in oil painting, cooking and exercise, among other activities.

Buglass estimates that only three or four of Arlington's 37 schools have no activities scheduled during the summer, mostly because of repair work or lack of air conditioning, such as at Stratford Junior High School on North Vacation Lane.

"Ten years ago, only 3 or 4 per cent of the use of a school was by those outside the school system," Buglass said. "Now it's grown to about 10 per cent on a year round basis. During the summer, the recreation department uses schools much more than the school system."

He added that "outside" use of the schools continues to increase about 5 or 6 per cent a year, coincidentally the same rate that Arlington's pupil population is declining.

In Fairfax, the recreation department operates playgrounds at 109 of the county's 167 schools. Playground operation requires use of the inside of school buildings for rest rooms and space on rainy days.

At Groveton High School on Quander Road, more than a thousand students from Fairfax County's Area I school district are attending summer school, which is also offered at three other Fairfax high schools.

When school finishes at 1:40 p.m., it looks like a regular school year is under way. Streams of students pour from the front doors to climb aboard a column of buses parked outside.

But within minutes, the dusty grounds surrounding the campus-like school are barren. All that is left are individual pupils being tutored inside and faculty members in a staff meeting.

The silence is broken about 5 p.m. when the adjacent recreation center opens. The "teen center" held there each weeknight features sports, table games and dances, and attracts a steady turnout of kids. Twenty other Fairfax schools also have teen centers through the summer.

Meanwhile, classes in typing, commodity futures, tumbling, voice, guitar, gymnastics, tennis and painting, among other subjects, are offered at different times of the day and evening.

"Only a handful" of Fairfax schools have no summer events scheduled, according to Dusty Rhodes of the county's safety department.

"We've got 44 schools with church services in them on Sundays; we've got extension courses from four universities; we got the Coast Guard, the Girl Scouts, civic groups," Rhodes said. "We've got so many things going on that the only ones who really know what is happening in the schools are the principals.

"You can say that by keeping a school open you're avoiding vandalism and saving the taxpayer money," he continued. "On the other hand, you keep it closed and you don't have expensive utility costs. As for vandalism, we had about $30,000 last year by people using the buildings."

Alexandria, unlike Fairfax and Arlington Counties, has no formal agreement between the school system and recreation department that outlines sharing of funds for operating jointly used buildings among the city's 18 schools.

"But the same sharing arrangement operates here," says Joseph McGowan, chief of general services for Alexandria schools. "At Mt. Vernon for example, the recreation department has its investment there as a community center, but the school uses the gym as its own during the regular school year."

About 630 pupils attend summer school at T.C. Williams High School, and other summer classes are taught seventh and eighth graders at Parker-Gray Middle School. Adult education classes are taught at T.C. Williams, Hammond High School, Minnie Howard Middle School and George Washington High School.

The recreation department operates playgrounds at eight schools and offers tennis lessons at eight schools, some of which are combined school-recreation facilities.

"Our schools are used much more by outsiders than they used to be," he added. "The money for recreation has multiplied several times over, and the needs of the community are changing. The schools are already there, and they ought to be used."