The bottom of the deep blue sea is exactly what the sailors aboard the Mt Mitchell hydrographic survey ship set out upon the sea to see on their cruises up and down the East Coast. This weekend you can board the National Oceanic and Atmospheric Administration's 231-foot ship down at Pier 1 at the Washington Navy Yard, talk to the crew and examine the ship and its research equipment used for collecting information for nautical charts.

Admission to the following activities is free unless otherwise noted.

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.

SHIP TOUR -- Saturday and Sunday, 10 to 4, Pier 1, Washington Navy Yard, Ninth and M streets SE. Come aboard the 231-foot Mt Mitchell, a National Oceanic and Atmospheric Administration survey ship, and explore the scientific equipment and talk to crew members. 433-2217.

OLD TOWN TOUR -- Saturday and Monday, 10:30 a.m.; Sunday, 2, Ramsay House Visitors Center, 221 King St., Alexandria. Take a special tour retracing the steps of George Washington and Robert E. Lee with a colonial- attired guide through the cobblestoned streets of Old Town Alexandria. Adults $3; ages seven to 15, $1.50. 548-0100.

CANAL TOUR -- Wednesday-Sunday, 10:30, 1 and 3; an additional tour Friday and Saturday at 5, C&O Canal National Historical Park, The Foundry Mall, 1055 Thomas Jefferson St. NW. Take a mule-drawn boatride on "The Georgetown" on the C&O canal. Adults $4; children and seniors $2. 472-4376.

ARTS AND CRAFTS EXPO -- Friday and Saturday, 10 to 6; Sunday, noon to 5, Hunters Woods Shopping Plaza, Colts Neck Road, Reston (take the Beltway to exit 10 west (Route 7), 7 miles to left at Route 606, 2 miles left at Route 602, left on Glade then left on Colts Neck Road to center). Thirty-five professional artisans will display their wares, which include sheepskins, calligraphy and pottery. 751-3050.

CREATIVE HOME SHOW -- Friday and Saturday, 10 to 9:30 p.m.; Sunday, noon to 5, Wheaton Plaza, Viers Mill Road between Georgia Avenue and University Boulevard, Wheaton. Featuring new ideas in home decorating as well as suggestions for buying or refinancing new homes. 946-3200.

VIRGINIA STATE FAIR -- Friday, 8 a.m. to midnight; Saturday, 10 a.m. to midnight; Sunday, 10 a.m. to 11 p.m., Fair Grounds, Richmond (take I-95 to exit 17 and follow signs for the fair grounds). Family fun including rides, shows, musicians and a wide variety of food. 804/329-4437.

RENAISSANCE FESTIVAL -- Saturday and Sunday, 10:30 to 6, Crownsville, Md. (take U.S. 50 east, then go north on Rte. 3, east on Rte. 450 to Crownsville Road, turn left for one mile to the festival site). Jugglers, jousters and magicians along with other 16th- century characters come alive in this salute to the Renaissance. Adults $7.50; Seniors $6.50; 13 and under $3.50; five and under free. 261- 1970.

VIRGINIA RELIEF SALE -- Saturday, 6 a.m. to 1 p.m., Augusta Expoland, Fishersville (take I-64 to exit 16, Fisherville, and follow signs). Join the Mennonites as they try to raise funds for needy people around the world. The day's activities will feature "self-help" crafts produced overseas, a homemade breakfast and lunch, two seperate auctions and a painting and clock sale. 703/943-8987.

CAT SHOW -- Saturday and Sunday, 9 to 5, Stamp Student Union Building, University of Maryland, College Park. Purebred cats, kittens and household pets compete. Adults $3; seniors and kids, $2. 302/445-1253.

NOTTOWAY FLEA MARKET -- Saturday, 9 to 3, Nottoway Park, 9601 Courthouse Rd., Vienna (take Beltway exit 9-A (I-66 west) to right on Route 243 to left on Courthouse, park entrance on left). Many household items and handmade crafts; refreshments for sale. 938-7532.

BOOK SALE -- Saturday, 10 to 3, Chevy Chase Library (two blocks below Chevy Chase Circle on Connecticut Avenue). Lots of books at low prices. 727-1341. MOONSHINING DEMONSTRATION -- Saturday and Sunday, 11 to 5, Catoctin Mountain Park, Thurmont, Md. (take I-270 north to U.S. 15 north and then Rte. 77 west which leads into the park; park at visitors center). A park ranger gives a continuous whiskey-making demonstration at the actual site of the Blue Blazes Whiskey Still. 301/663- 8687.

CRAFT AND FUN FESTIVAL -- Saturday, 10 to 3; Sunday, 1 to 5, Mason District Park, 6621 Columbia Pike, Annandale. (Beltway exit 6E, Little River Turnpike, Route 236, east two miles to left at Columbia Pike to park entrance). Festivities include an arts and crafts fair, pet show, food and special appearances by Big Bird and Woodsy the Owl. 941-1730.

TRI-MOUNTAIN WINE FESTIVAL -- Saturday and Sunday, 1 to 5, Tri-Mountain Winery and Vineyards, Middletown, Va. (I-66 west, then I-81 north to exit 77, then east one mile to the Winery). Take a tour of a winery, stomp down on some grapes or just enjoy tasting the wine while snacking on cheese and crackers. Adults $3; under 21, $1. 960-9326.

SHOWCASE & HARVEST FESTIVAL -- Harvest Festival, Saturday, 11 to 4; Showcase, Sunday, noon to 5. Harvest Festival, Meredith House, Dorchester, Md. (From U.S. 50 East, turn east on Maryland Avenue, three blocks to Meredith House). Showcase, High Street, Cambridge (from U.S. 50 east, turn west on Maryland Avenue across Cambridge Creek, go right on Spring Street to High Street). Saturday enjoy displays of quilts, crafts and fresh produce. Then on Sunday stroll down Cambridge's historic High Street where more than 70 artists and craftsmen will exhibit and demonstrate their goods. 301/228-7782.

LIVE AT THE GAZEBO -- Sunday, 1 to 3, Takoma Park Gazebo, Cedar Lane, Takoma Park. This year's "Live at the Gazebo" outdoor concert series opens with "Magpie" playing a variety of contemporary and traditional folk, blues, ballads and classics. 270-1700.