Along with the various balls, bats and bikes sported around town these days, you can bet there are enough Frisbees to keep Mr. and Mrs. Whamo deep in the money. This weekend, Frisbee fans might head to Virginia for the 8th annual April Fools Ultimate Frisbee Festival. Ultimate Frisbee is kind of like soccer, except players can't run with the disc. Thirty-six teams have signed up for this weekend's competition, including New York's "Kaboom," the 1984 men's champions; Michigan's "Fishheads," the women's champions; and even the "Walking Canes" from West Germany. There'll also be demonstrations by Frisbee- catching dogs and Frisbee freestylers. The competition begins with quarterfinal matches from 9:30 a.m. to dusk on Friday and Saturday. Semifinal rounds start at 9:30 a.m. Sunday, followed by the women's final at 1 and the men's final at 3. The quarter- semifinals will be held at Bull Run Regional Park in Manassas (off I-66 in Centreville). The action moves to McLean High School, 1633 Davidson Road in McLean, at 1 p.m. Sunday. To get to the school, take Route 123 east off the Beltway, turn right on Chain Bridge Road, right on Davidson Road. Call 734-7026; $1 donation requested.