Elizabeth Tillett MacAgy, 50, a former researcher for a communications and consulting film production company and co-author of a children's book about modern art, died of spinal meningitis Sunday at George Washington University Hospital.

Mrs. MacAgy had lived in Washington since 1968, when her husband, Douglas A. MacAgy, became deputy director of the National Endowment for the Arts. Mr. MacAgy later was curator of exhibitions for the Hirshhorn Museum and Sculpture Garden. He died in 1973.

From 1972 until 1977, Mrs. MacAgy worked for Robert M. Johnson Associates and was director of research for "The American Adventure Theater," a film project produced in connection with the Bicentennial. She was a freelance researcher after leaving the Johnson firm.

Mrs. MacAgy was born in New York City and grew up there. She graduated from Goucher College and then went to Paris, where she worked on the Paris edition of The New York Herald Tribune in the late 1940s. After returning to New York, she worked for the Museum of Modern Art.

In 1955, she married. In 1959, Mr. and Mrs. MacAgy published "Going For a Walk with a Line," a book for children about modern art. The couple lived in New York and Dallas before moving to Washington.

Mrs. MacAgy's survivors include a daughter, Caitlin E. MacAgy, of Boston, a son, Ian D., of Washington, and her mother, Mrs. W. S. Tillett, of Chester, Conn.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society.