Talk about a hard act to follow. Kathleen Chalfant won an OBIE, a Lortel Award, a Drama Desk Award and Outer Critics Circle Awards for her role in Margaret Edson's Pulitzer-winning drama, Wit. But all great things come to an end, and Chalfant leaves the Off-Broadway drama, as scheduled Aug. 8.

Filling her enormous shoes, beginning Aug. 10, will be Judith Light, best known for her eight years on ABC-TV's "Who's The Boss." (Light's television co-star, Tony Danza, is currently in another high-class New York play: The Iceman Cometh). Her stage credits include playing the maid in a 1975 Broadway mounting of Ibsen's A Doll's House (opposite Liv Ullman and Sam Waterston), as well as the Broadway play Herzl.

After her first legit gig -- Adelaide in a USO tour of Guys and Dolls -- Light spent full seasons at Milwaukee Rep, Seattle Rep and the California Shakespeare Festival.

Light will join other current cast-members Walter Charles, Brian J. Carter, Alec Phoenix, Paula Pizzi, Helen Stenborg, Maya Thomas, Daniel Sarnelli and Lisa Tharps.

Wit, playing at the Union Square Theatre, tells of a strict college poetry professor brought low -- to humility and humanity -- by her bout with ovarian cancer. A national tour of the show is planned for January January-September 2000, but no casting has been announced. For tickets and information on Wit, directed by Derek Jones, call (212) 307-4100.

-- By David Lefkowitz