In spite of the chill, this is a good weekend for getting out into the woods. You can learn about what the animals are doing to keep warm; or follow a duck long enough to identify its species; or try to navigate the woodlands using a map and a compass. And if you're feeling really adventurous, you can join in a simulated wolf hunt.

Admission to the following activities is free unless otherwise noted.

EXERCISE FOR SENIORS -- Friday, 10 to 10:45, St. Patrick's Episcopal Church, Whitehaven Parkway NW. Women over 60 can exercise and dance to music, weekly. $10 donation suggested for annual membership. 966-1055.

COMET HALLEY WATCH -- Friday, Saturday and Sunday, 6:30 to 8:30, Braddock Road Park, 13241 Braddock Rd., Clifton, Va. Join members of the Northern Virginia Astronomy Club to view Halley's approach. Binoculars recommended. 631-0013.

WATERFOWL HIKE -- Saturday, 9:30 to 11:30, Riverbend Park, 8800 Potomac Hills St., Great Falls, Va. Look for bird species along a two-mile path. Binoculars and bird guide recommended. 759-3211.

WILDLIFE HIKE -- Saturday, 10 to noon, Red Rock Wilderness Overlook Park, Edwards Ferry Road, Leesburg. Track animals by observing vacated nests, deer rubbings and trails. Binoculars recommended. 528-5406.

CIVIL WAR CAMP -- Saturday, 10 to 3, Fort Dupont Park Activity Center, Minnesota Avenue and Randle Circle SE. Hear the stories from both sides in a living history exhibit. 426-7745.

BEER-CAN SWAP -- Saturday, 11 to 3:30, Bethesda Community Recreation Center, 4506 Walsh St., Chevy Chase. Buy, sell or trade at a collectors' swap meet. General admission: 50 cents; adult traders, $1.50; traders ages 17 and under, $1. 468-4210.

ROCK CREEK MILLS -- Saturday, 11, Pierce Mill, Beach Drive and Tilden Street NW. Learn about the mills that once dotted the creek. 426-6829.

ORIENTEERING -- Saturday, 11, Prince William Forest Park, Route 619 west off I-95, Triangle, Va. A talk on using maps and compasses is followed by a chance to try them out on a course. 703/221-2104.

HOLIDAY PLANTS -- Saturday, noon to 2, U.S. Botanic Garden, First Street and Maryland Avenue SW. Find out how poinsettias, Easter lilies, cyclamens and amaryllis can survive past the holidays. 225- 7099.

ELVIS FANS UNITE -- Saturday, 1 to 4, the Presley Museum at Potomac Mills Mall, 2700 Potomac Mills Circle, Woodbridge, Va. A celebration of the late Elvis Presley's 51st anniversary features the lead singer from his back-up band, birthday cake, door prizes/memorabilia and a cardboard look-alike figure. 643-1203.

TOOTH AND CLAW -- Saturday, 7:30 to 9:30, Gulf Branch Nature Center, 3608 N. Military Rd., Arlington. A slide show about how animals hunt for their food precedes a study of wolf habits and hunting calls. Warm clothing is recommended. 558-2340.

SQUARE DANCE -- Saturday, 7:30 to 10, Fairfax United Methodist Church, 10300 Stratford Ave., Fairfax. For dancers of all levels. $1 donation suggested. 591-3120.

SIERRA CLUB DANCE -- Saturday, 8 to 10:30, Arlington Forest Methodist Church, U.S. 50 and N. Henderson Street, Arlington. Square dance for beginners and singles. $4. 430-9006.

IRISH DANCE -- Saturday, 8:30, St. John's Church, 5700 Sargent Rd., Chillum, Md. A ceili; music by Tim Mulcahy. $6. 241-1978.

RECORD CONVENTION -- Sunday, 10 to 6, Crowne Plaza Holiday Inn, 1750 Rockville Pk., Rockville. The Vinyl Event features recordings in rock, jazz, soul, pop and country music. $2. 589-0843.

TEA PARTY -- Sunday, 2, National Colonial Farm, 3400 Bryan Point Rd., Accokeek, Md. Preparations of herbal teas provide an opportunity for tasting. $2.50 for members, $3.50 for non-members. For reservations, call 283-2113.

ART AUCTION -- Sunday, 8, Silver Spring Jewish Center, 1401 Arcola Ave. Silver Spring. Preview of the art is at 7; $2.50 donation suggested. 649-4425.