For the past two summers 12-year-old John Pettit of Alexandria, and many other youngsters interested in sports, have benefited from coaching fit for top college champions.

During John's five summer days at the University of Virginia Basketball Camp, he practiced under the direction of head coach, Terry Holland, assisted by Holland's staff, as well as top high school coaches and NBA and U-Va. players.

"Some of the campers hadn't played basketball before," says John, "but after five days, they could." He discribed dorm life as "fun" and the food, "great."

Mornings are devoted to developing individual skills; afternoons to team play. For league play, teams are balanced between beginners and experienced players. Winding up the week is a championship tournament.

During the summer many college coaches, like Holland, rent university facilities to run children's sports camps, offering top training equipment and coaching staffs. From Monday to Friday, for six, or more hours a day, the campers indulge in their favorite sport. They learn the fundamentals, hear lectures, watch films and . . . practice, practice, practice. Coaches frequently use video tapes to help camper interpret strengths and weaknesses.

Some camps are for boys or girls only; others are coed. Each sets its own age requirements, ranging from age 7 to 18-year-olds entering their high schoold senior year.

Along with dormitory life, boarders eat at the training table, many billed as "all you can eat." Campers tend to rave about the food; their parents rave about the close supervision. (Free-time activities range from ice-cream parties to walking tours of the campus' surrounding area.) And there is, of course, always the hope that the coach will remember a child in the future when scholarships are awarded.

Virtually every sport is offered on some college campus, either in the form of a day or boarding camp; baseball, basketball, cheerleading, conditioning, diving, field hockey, football, golf, gymnastics, hockey, lacrosse, "pitchers and catchers," soccer, softball, swimming, tennis, track, volleyball and wrestling.

Costs range from $120 to $260 for five days of room, board and instruction: day camps from $50 to $125. Some camps offer discounts for teams.

In addition to the basketball camp at U-Va., Holland offers a session at Graves Mountain in the Blue Ridge Mountains, where campers live in cabins along a mountain stream and eat at Grave Mountain Lodge.

Boys 8 to 18 may attend head coach Lefty Driesel's University of Maryland Basketball School on the Maryland Basketball School on the Maryland campus."Over the past [16] summers," says Driesell, "we've had many players that became high school stars, receive college scholarships, and some are playing in the NBA."

But the primary purpose, he says, is to teach young people the fundamentals and to stress "the ideals of team play and sportsmanship."