He already has experienced the thrill of winning a state championship. His college scholarship has been signed. He has little to prove about the extent of his athletic ability, yet, Glenn Williams is finishing his nine-letter athletic career at T.C. Williams playing baseball.

Williams, a 6-foot, 165-pound senior, is a near-extinct breed of high school athlete in that he not only plays but also excels in three sports. Last fall, he quarterbacked the Titans to the state AAA football title, and last month he signed a basketball letter-of-intent with Holy Cross.

Although he admits feeling drained from his overlapping seasons, a part-time job, and the time required to maintain an academic average above 3.0, Williams says there was never a doubt he would remain active during his final months in high school.

"I sometimes thought about playing just one sport, like basketball because it's my favorite, and trying to be the best at that," said Williams, who hit .292 with eight RBI and eight runs scored as the Titans went 4-4 in their first eight baseball games this spring. "But I always knew when baseball season came around, I would want to be out there playing baseball."

T.C. Williams basketball Coach Mike Hynson believes athletes should play a variety of sports rather than concentrating on only one.

"I'm all for it, but I guess I'm from an era when people played as many sports as they were capable of," said Hynson. "I think it may hurt a little as far as any one particular sport, but playing different sports is better for them as a person."

Williams will stick to basketball as a Holy Cross freshman, but he has already talked with coaches about additionally playing either football or baseball in his sophomore year.

The National Federation of State High School Associations, at its recent meeting in Kansas City, enacted a number of rules changes for the 1985-86 basketball and wrestling seasons.

The most significant basketball change provides for adoption of a smaller ball for girls as is now used at the collegiate level. The state of Virginia probably will start using the smaller ball next year.

In addition, the national rules committee passed a measure allowing states to decide if they want to award three points for shots beyond 19 feet. Virginia has not acted on this proposal.

Another change, effective for boys and girls next year, will have alternating possession in what are now jump-ball situations.

For wrestlers, one change will have weigh-ins one hour prior to tournaments rather than the 2 1/2 hours now mandated. Another wrestling change limits heavyweights to 275 pounds, regardless of additional weight classes.