The Friday Morning Music Club, celebrating its centennial this year, presents trumpeter Mark Henrikson, organist Charles Callahan, mezzo-soprano Deborah Kieffer with pianist Frank Conlon, and duo pianists Bonnie Kellert and Barbara Wing at its free opening concert Friday at noon, New York Presbyterian Church, 1313 New York Avenue. 558-1895 . . . The Black American Collectibles Show and Sale is Saturday from noon to 8 and Sunday from 11 to 6 at Armory Place, 925 Wayne Avenue in Silver Spring. $3. 726-8931 . . . The American Chamber Orchestra holds a free concert with cellist Glenn Garlick Saturday at 3 in the Anderson House ballroom, 2118 Massachusetts Avenue NW. 785-0540 . . . Bob Hope will appear at George Washington University's Smith Center Saturday from 8 to 10; tickets are $17.50 and $20. 676-7270. IN MARYLAND
The United States Powerboat Show at the City Dock and Harbor in Annapolis is Friday and Saturday, 10 to 7, and Sunday, 10 to 6. $6, $3 for children under 12. 301/263-8950 . . . The Maryland Medieval Mercenary Militia reenacts the battles of Stamford Bridge and Hastings Saturday at 10 a.m. at the University of Maryland's College Park Campus. 301/262-9466; free. IN VIRGINIA
Clifton, Virginia, celebrates Clifton Day with an art show, antique sale, crafts and food Sunday from noon to 6. Call 703/631-1081 for directions and information.