Cora J. Thomas, 80, volunteer worker for many years with mental patients at Western State Hospital in Staunton, Va., died Tuesday at the Barcroft Institute in Falls Church, where she had lived for three months. She had been in failing health for some time.

Born in Alexandria, Mrs. Thomas had spent most of her life there, living in Washington for a period in the 1930s and 1940s.

She became active in the well-being of patients at Western State after a son, Robert S., became a patient there. Known to the patients as "Rambling Rose," she continued to visit and help them after her son was released.

Eventually her work led to the organization of a Robert S. Thomas Club in this area in which other families became involved. Mrs. Thomas and the club were cited by the Foundation for Community Aid to Mental Patients.

In addition to her son, Robert, she is survived by three other sons, Chester A. Thomas, of Clinton, Md., Herbert L. Koch, of HIngham, Mass., and Joseph M. Thomas, of Fairfax; four daughters, Charlotte M. Hall, of Oxon Hill, Barbara Ann Ruddy, of Los Angeles, Rita M. McCoy, of Winchester, Va., and Doris M. Gryder, of Fairfax; a sister, Leola Zimmerman, of Alexandria, and 22 grandchildren.

The family suggest that expressions of sympathy may be in the form of contributions to a patient fund at Western State Hospital.