Pedal in the 6th Annual Bike For Sight, a five-mile bicycle ride, Saturday from 9 to noon beginning at the Tidal Basin in West Potomac Park. Registration is at 8:30. Free. 234-1010 . . . The Spirit of Massachusetts, a 125-foot schooner, docks at Gangplank Marina and makes its decks available for a free open house Saturday and Sunday from 9 to 3. The marina is at 600 Water Street SW. 554-5000 . . . Final auditions of the 1986 Washington International Competition for Singers are Saturday from 11 to 4 in the Kennedy Center Concert Hall. Free. 588-1895 or 628-2264 . . . The Concert Hall is also the scene for a performance by flutist James Galway, who accompanies the National Arts Center Orchestra of Canada Saturday at 8:30. Tickets range from $5 to $27.50. 432-0200 or 393-3600 . . . Dancers of the Silver Screen, a live performance of classic dance styles by LaVaughn Robinson and the Philadelphia Tap Dancers, is Sunday at 3 in Baird Audtitorium, Museum of Natural History, 10th Street and Constitution Avenue NW. Tickets are $10 for adults, $6 for children under 13. 357-3030. IN MARYLAND
Some 200 powerboats and sailboats are afloat on the Chesapeake Bay at the Sandy Point Boat Show (in Sandy Point Park off U.S. 50 at the last exit just before the Bay Bridge). The show runs Friday through Sunday from 10 to 6. Admission is $5. 301/757-6676. IN VIRGINIA
This country's largest all-breed dog show (4,000 dogs last year) is Saturday from 8 to 3:30 at Bull Run Regional Park, three miles west of Centreville on 7700 Bull Run Drive, Centreville. Admission is $2.50; 50 cents for children. 703/790-9787 . . . The Arlington Metropolitian Chorus performs Cries of London: Four Centuries of English Choral Music Sunday at 3 at Westover Baptist Church, North Patrick Henry Drive and Washington Boulevard in Arlington. Tickets are $6.50, $4.50 for students and seniors. 739-2922.