Mary Smith MacCaulty, 55, a former resident of Montgomery County, died of cancer Friday at her home in Little Cove, Pa., where she had resided since 1976.

Prior to moving there, she had lived near Clarksburg, Md. She was the wife of Thomas MacCaulty, retired information officer for the Atomic Energy Commission and former staff member of the Senate Republican Policy Committee.

Mrs. MacCaulty was born in Belding, Mich. She was the daughter of Betty Smith, who later became the well-known author of "a Tree Grows in Brooklyn," and other novels and plays.

Mrs. MacCaulty moved to Chapel Hill, N.C., as a girl and later attended the University of North Carolina there. She also was proprietor of an antique shop in Chapel Hill before moving here.

After moving to Pennsylvania, she wrote a food column, "gourmet Grandma," for the Chambersburg (Pa.) Public Opinion.

In addition to her husband, she is survived by three children by a former marriage, Candace Nordan, of Atlantic Beach, Fla., John Carroll, of Fannettsburg, Pa., and Bonnie Ernst, of Hagerstown, Md.; a sister, Nancy Pfeiffer, of New Haven, Conn.; two stepsons, Dr. T. Cameron MacCaughelty, of St. Louis, Mo., and Robert J. MacCaughelty, of Charlotte, N.C., and one grandchild.