Reconstruction of a crucial portion of Broadway has been rumored for two years. But now it looks like changes are afoot. Current tenants of the Judith Anderson, INTAR, Samuel Beckett, and Harold Clurman Theatres, four pillars of West 42nd Street’s Off-Broadway Theatre Row, are on month-to-month leases. The theaters may be virtually demolished in early 2000 to make room for a modern complex containing six new theatres topped by an apartment tower. Backstage