Deft comedienne who, two years out of college, began her professional career playing sardonic, chubby Brenda Morgenstern, younger sister to Valerie Harper's title character on the long-running TV sitcom "Rhoda" (1974-78). With her wry, sarcastic delivery, her ethnic, raspy and slightly nasal whine and her self-deprecating humor, Kavner has carved a niche as a likable second banana, playing scrappy underdogs, working women and supportive wives in such films as "Bad Medicine" (1985), "Surrender" (1987) and "Awakenings" (1990), TV-movies like "No Other Love" (1979) and "Revenge of the Stepford