Marjorie Mazia Guthrie, who began her career as a dancer but who, in the last 15 years of her life, devoted herself to creating an awareness of Huntington's chorea - a disease that killed her husband, the folk singer Woody Guthrie - died of cancer at her home yesterday. She was 65 years old, and lived in Manhattan.

At the end of her life, Mrs. Guthrie was working on a plan, through the foundation named for her husband, to establish a neurologic wing for research and care at the Helen Hayes Hospital in Haverstraw, N.Y. Huntington's chorea is hereditary and leads to a protracted deterioration of the brain.

In 1967, after the folk singer died, Mrs. Guthrie founded the Committee to Combat Huntington's Disease. It was her hope that treatment would be made available, a cure would be found and families afflicted by the disease would be assisted. Impact on Her Own Family

In her own case, once the full impact of Mr. Guthrie's illness on herself and her family was felt, Mrs. Guthrie divorced her husband. She continued to care for their three children and spent much time with him in various hospitals. She taught him to communicate by blinking his eyes, after he had lost control of his other muscles.

''We agreed that we didn't need a piece of paper to hold us together,'' Mrs. Guthrie told an interviewer in 1977. ''I never really divorced him in my heart and in my actions. Divorce was an opportunity for me not to be financially responsible for his hospitalization.''

She raised money to pay for publication of the first bibliography of articles on the disease, by the University of Leiden Press in the Netherlands. Through her committee, families in which the disease was present were identified. The first year there were six; now there are almost 10,000.

Mrs. Guthrie was also instrumental in creating the World Federation of Neurology's Research Commission on Huntington's Chorea. She headed a Federal commission for control of the disease in 1976 and 1977, and lectured to medical students about the illness and how it affects the patient and the patient's family. Member of State Agencies

She also headed the public and governmental information committee of the National Committee for Research in Neurologic and Communicative Disorders, was a member of the New York State Commission on Health Education and Illness Prevention and of the state's Genetic Advisory Committee, and was a lay member of the advisory council of the National Institute of General Medical Science.

Mrs. Guthrie danced with Martha Graham in 1935, under the name of Marjorie Mazia, and became Miss Graham's first assistant in the Graham School of Dance, a position she held for 15 years.

In 1975, Mrs. Guthrie married Martin B. Stein, who was vice president of the Committee to Combat Huntington's Disease. He has since died.

Mrs. Guthrie is survived by two sons, Joady and the folk singer Arlo Guthrie; a daughter, Nora Rotante; three brothers, Herbert Greenblatt of Pompano Beach, Fla.; Dave Greenblatt of New York and Bernard Greenblatt of Las Vegas; a sister, Gertrude Mazia of Berkeley, Calif., and six grandchildren.

Marjorie Guthrie