In honor of Martin Luther King, Jr.'s birthday this Saturday, there are a number of celebrations and observances in town: Mayor Marion Barry makes the fifth annual parade, to begin Friday at 9 at 2041 Martin Luther King Jr. Avenue SE. The King Day Parade goes to Covenant Baptist Church 3845 South Capitol Street SW, where area children offer their tributes. Mayor Barry will also attend Washington's official annual observance at 10 at M.L. King Memorial Library; that will include music and tributes by Floretta MacKenzie and other city officials. Free at Ninth and G streets NW. At 10:30 that day, the fourth annual celebration of the D.C. Maryland Regional Office of the Anti-Defamation League of B'nai Brith and the YMCA will be on the eighth floor of the B'nai Brith Building at 1640 Rhode Island Avenue NW. The two- hour affair includes the film "Martin Luther King: From Montgomery to Memphis" and essays and posters by students honoring the man. Free admission. The same film will be shown Friday at 10 and 1:15 at the Anacostia Neighborhood Museum, 2405 Martin Luther King Avenue SE. Free admission; call 287-3369. Ten local and international groups commemorate King's birthday Saturday in Rockville's annual community festival. There'll be international dancing, food and art by students dedicated to King, noon to 4 at the Rockville Senior Center. Free admission at 1150 Carnation Drive in Maryland. Call 340-7225. And there'll be music and tributes to the man and his work in a memorial program at 7:30 at the First Christian Church; free at 2723 King Street in Alexandria.