Miss Lonergan, whose grandfather, father and brother also were actors, made her stage debut at the age of 6, in ''Mother Lode,'' starring Melvyn Douglas. In 1939, she played Dinah Lord, the younger sister of Katharine Hepburn's Tracy Lord, in Phillip Barry's comedy ''The Philadelphia Story.'' In The New York Times, Brooks Atkinson wrote of Miss Lonergan's performance, ''As the brat of the family, Lenore Lonergan, of a famous theatrical tribe, acts with a stout sort of humor that suits her groaning little figure.''

Miss Lonergan also played juvenile roles in ''Junior Miss,'' by Jerome Chodorov and Joseph Fields, and in ''Dear Ruth,'' by Norman Krasna. She appeared in ''Crime Marches On,'' ''Fields Beyond,'' and in the film ''Tom, Dick and Harry,'' among others.

-The New York Times