Saturday's the perfect day to get all wet at Patuxent River Park's "11th Annual Jug Bay Raft Regatta" in Prince George's County.

You can register up until the gun goes off, and there are few rules regarding the type of raft you can use -- anything that appears to be safe and floats may be entered upon inspection by the Marine Police. Everyone's required to wear a life jacket; a limited number are available from the park, but bring your own if you've got one.

The two-mile race starts at Jackson's Landing and ends downriver at Selby's Landing. Awards will be given for speed, overall originality and panache. The famous Commodore Barney Award goes to the raft that sinks or disintegrates with most style.

Admission to the following activities is free unless otherwise noted. 4-H FAIR DAYS -- Friday, 9 a.m. to 9 p.m.; Saturday, 8 a.m. to 4 p.m., 4-H Fairgrounds, on Rte. 699 (Take Rte. 7 west; 3 miles west of Leesburg take Hillsboro-Charles Town exit Rte. 9, make left at stop sign at top of ramp, follow signs to Rte. 699 and fairgrounds). "50th Annual Loudoun County 4-H Days." Exhibits, horse shows, pie-eating contest, border collie demonstration, livestock sale and more. For schedule, call 703/777-0373.

SENIOR CITIZEN PARTY -- Friday, 10 a.m. to 2, Good Luck Community Center, 8601 Good Luck Rd., Lanham. Dancing, ceramics, exercise and needlework. Bring a lunch and a friend. 552-1093.

KILN EXPLOSION -- Friday and Saturday, 10 to 5, Appalachiana, 10400 Old Georgetown Rd., Bethesda, "Fourth Annual Pottery Sale." An opportunity to purchase work from area craftsmen, including the results of excess stock, experimentation, aesthetic disappointments and just plain seconds. 530- 6770.

OLD TOWN TOUR -- Friday, 8 p.m.; Saturday, 10:30 a.m., 8 p.m.; Sunday, 2, Ramsay House Visitors Center, 221 King St., Alexandria. Take a special summer tour retracing the steps of George Washington and Robert E. Lee with a colonial-attired guide through the cobblestone streets of Old Town Alexandria. Adults $2; ages seven to 15, $1. 548-0100.

PLAYING HOUSE -- Saturday, 10 to 5; Sunday, noon to 4, Holiday Inn, 2 Montgomery Village Avenue (across from Lake Forest Mall), Gaithersburg, "Dollhouse Miniatures Show and Sale." Adults $3; under 12, $1.50. 301/948-8900.

RAFT RACE -- Saturday, noon to 4, Patuxent River Park, Jackson's Landing, Patuxent River, near Croom, Md. (take Rte. 4 west to U.S. 301 south four miles to Croom Road, turn left four miles to Croom Airport Road, follow signs to park office). "11th Annual Jug Bay Raft Regatta." Registration up until race time. 627-6074.

ART IN THE PARK -- Sunday, noon to 7, Malcolm X Park, 16th Street and Florida Avenue NW, "19th Annual Art in the Park" exhibit. Artists display their paintings, sculptures, crafts, photography and other works for sale. Live musical entertainment throughout the day. 820-1188.