Hound dogs take to the woods this weekend for a coon hunt Friday and Saturday near Manassas. On either evening you can comb the woods after 9 o'clock (until 5 a.m., if you wish) behind a party of hound dogs and hunters. No live game will be taken; winners are selected according to the total number of points based on how many raccoons are treed.

Saturday features a water race with hounds baying and charging through a pond toward a stuffed coon; a dog show featuring seven different breeds; a barking auction where you bid on the dog you think can bark the most in thirty seconds; a barbecue and more. The Old Dominion Coon Hunters Association sponsors this free event as a benefit for the Children's Rehabilitation Center at the University of Virginia.

The following activities are free unless otherwise noted.

CALLING ALL TREKKIES -- Friday and Saturday, 10 a.m. to 2 a.m.; Sunday, 10 a.m. to 6 p.m., the Marriott Tysons Corner, 8028 Leesburg Pike, Vienna (take Beltway to exit 10-B), "Star Trek Convention." Sci-fi films, panel discussions and exhibits. Admission is $8 Friday and Sunday; $9 Saturday; $15 for the entire weekend. 937-5057.

ANTIQUE SUPERMARKET -- Friday, noon to 9; Saturday, 11 to 9; Sunday, 11 to 6, D.C. Convention Center, New York Avenue between Ninth and 11th streets NW, "Antique Show and Sale." More than 100 dealers exhibit a wide variety of antiques and collectibles. $3. 371-3080.

COON HUNT -- Friday, 5; Saturday, 1; Old Dominion Clubhouse, Rte. 608, 12 miles south of Manassas (take I-95 south to Rte. 234 west turning left on Aden Road; follow UKC Event signs to clubhouse), "Second Annual Coon Hunt." Join a hunting party for a midnight tromp through the woods either evening; bring boots and flashlight. Saturday at 1 there'll be a dog race through the water, dog show, bark auction, barbecue and more. 960-4894.

4-H FAIR -- Friday, 7; Saturday-Sunday, 9 to 5, Frying Pan Park, 2705 West Ox Rd., Herndon, Va. (take I-66 to U.S. 50 west to Chantilly, make right on Centreville Road and then on West Ox Road), "Old-Fashioned County Fair." Opening ceremonies and square dance Friday evening; 4-H projects, exhibits, entertainment, crafts show, food and more on Saturday and Sunday. 691-3400.

ZODIAC TALK -- Saturday, 9:30 a.m., Albert Einstein Planetarium, National Air and Space Museum, Sixth Street and Independence Avenue NW, "The Circle of Life." Explore how the rotation of the earth affects the relationship between the constellations and signs of the zodiac. 357-2700.

STREET FESTIVAL -- Saturday, 10, Anthony Bowen Elementary School Auditorium, Delaware Avenue and M Street SW, "Southwest Community Street Festival." Games, food, kids, arts and crafts, live music, fashion show and the Miss Southwest Pageant. 488-3746.

BUTERFLY SPYING -- Sunday, 9 to 11 a.m., Riverbend Nature Center, 8814 Jeffery Rd., Great Falls, Va. (Georgetown Pike west to right on Riverbend Road; right on Jeffery Road, right on Potomac Hills Street; follow signs to nature center). Join a naturalist on a one-mile hike through a field of wildflowers to find butterflies. 759-3211.

RECORD CONVENTION -- Sunday, 10 to 8, Tyson's Westpark Hotel, Rte. 7, one mile west of Beltway Exit 10. More than 80 dealers display thousands of records and music memorabilia; door prizes and free parking. $2. 237-4611.

CULINARY ARTS FESTIVAL -- Sunday, noon to 8, Washington Convention Center, New York Avenue between Ninth and 11th streets NW, "16th Salon of Culinary Arts." Chefs, bakers and cooks from over 40 local hotels show off their talents; you can look at their work, but not eat it. $3. 977-8133 or 371- 3080.

HEIRLOOM DISCOVERY DAY -- Sunday, 1 to 6, Shady Grove Adventist Hospital, 9901 Medical Center Dr., Rockville. Pull your hidden treasure out of the attic for a chance to have it appraised by experts. $5 per item. 279-6534.

WOODCARVING LESSONS -- Sunday, 1 to 4, Colvin Run Mill Park, Rte. 7, five miles west of Tysons Corner. The Woodcarvers of Northern Virginia will be on hand to teach you how to whittle small animals, birds and decoys. Tools are lent free of charge; there's a minimal fee for supplies. 534-1845 or 941- 7064.

HOMEMADE JELLIES -- Sunday, 1 to 4, Sully Plantation, Sully Road, Chantilly (take U.S. 50 to Route 28, which is Sully Road; park entrance less than a mile on right). Staff members demonstrate the art of making jelly over an open hearth, then let you taste it on a hot, buttered biscuit. Admission includes tour of house; $2 adults; $1 seniors and children. 437-1794.