Maybe Fred Astaire in top hat and tails comes to mind when you think of tap, but its origins were far from genteel: before the Civil War poor white laborers introduced black slaves "leased out" as stevedores on the banks of the Mississippi to the Irish Jig and Lancaster clog dances; boards on top of bales served as impromptu stages. William Henry Lane--"Master Juba," as he was known--first performed as a jig-and-reel dancer in the 1830s in the Five Points district of New York City, an area of brothels and tenements occupied by the Irish as well as blacks. But by 1848 Juba was performing in Vauxhall Gardens, London: the suave guy in suit and snappy shoes is equally a part of the tap tradition. This week Lane Alexander, director of Alexander Michaels/Future Movement, celebrates the history and future of tap in the fifth annual Human Rhythm Project, dedicated to the memory of his partner, Kelly Michaels. Teaching and performing this year are such old-timers as Chicagoan Jimmy Payne and Lloyd Storey, who danced with Bill "Bojangles" Robinson in the 40s and whom Alexander describes as smoother than Charles "Honi" Coles. And then there's Jan Feager--the director of Tapsichore in Saint Louis, known for her technique and sense of humor--who will perform pregnant. Think of it as a feast of tap, these and a dozen other individuals and groups performing a different program each night. Free performance next Thursday, July 20, at 12:15 in the auditorium of the Harold Washington Library, 400 S. State; regular performances Thursday at 7:30 and next Friday and Saturday, July 21 and 22, at 8 in the same place; $25. Workshops begin Monday, July 17. Call 559-1212 for tickets, 761-4889 for information.