Dr. John R. Cavanagh, 76, a prominent Washington psychiatrist for more than 40 years before retiring in the mid-1970s and an active Catholic layman who had taught at area universities and been active in professional organizations, died of congestive heart failure Saturday at his home in Washington.

Dr. Cavanagh taught courses in clinical medicine, psychiatry, and general medicine at Georgetown University from the early 1930s to mid-1940s. He lectured at Catholic University on pastoral medicine and psychiatry at Catholic University from the late 1930s to early 1970s, and also had taught at Trinity College here.

He was the author of more than 100 technical works, including the books "Fundamental Psychiatry" and "Fundamental Marriage Counseling: A Catholic Viewpoint." Other works included "Counseling the Homosexual" and "The Popes, The Pill, and The People."

In addition to his private psychiatric practice, teaching, and writing, Dr. Cavanagh devoted much of his time to the Catholic Church. He was named to the Papal Commission on Population and Birth Control in 1964, and over the years spoke out on the need for birth control in specific instances. These included marriages where an unwanted child would put undue stress on the marriage or create extreme mental anguish in a parent.

In a 1966 magazine article he was critical of the "rhythm" method of birth control and its imperfections. He wrote that cases he had studied and patients he dealt with "made me wonder if God intended Catholics to suffer so."

Dr. Cavanagh also offered advice in a slightly lighter vein, although the advice was no less radical, at least to some. In a 1957 speech at a District Social Hygiene Society luncheon he advocated the abolition of the traditional honeymoon.

"Honeymoons are not only expensive but frequently fatiguing, boring and a disappointing experience," he said. Dr. Cavanagh went on to point out that the honeymoon "may make or break a marriage." He also said newlyweds possess anxieties about intial sexual contacts. His solution? Dr. Cavanagh declared that "the best advice which can be given concerning the honeymoon is to spend it at home."

He had been a member of the National Catholic Welfare Conference since 1957, served as chairman of the National Conference of Catholic Bishops' committee on hospital directives in the early 1970s, and as president of the National Federation of Catholic Physicians Guilds in the mid-1970s.

In 1941, Dr. Cavanagh was named Knight Commander of the Order of St. Gregory, by Pope Pius XII, for his leadership as a Catholic layman and his devotion to the sick and poor.

Dr. Cavanagh was born in Brooklyn and came to Washington at an early age. He was a 1924 graduate of Gonzaga College High School and earned both undergraduate and medical degrees at Georgetown University. He interned in Providence Hospital and did post-graduate work in psychiatry at the University of Pennsylvania. He served with the Navy during World War II and attained the rank of commander.

He served on the D.C. Medical Society's Mental Health Committee in the 1950s and 1960s, and chaired the Society's annual assembly in 1941.

His wife of 42 years, Albertina Barth Cavanagh, died in 1975.

Dr. Cavanagh's survivors include three daughters, Patricia C. Anger of Piedmont, Calif., Judith C. Stoll of New York City, and Maria C. Johnson of La Canada, Calif.; a brother, Edgar J., of Staten Island, N.Y.; a sister, Mary R. White of Greenbelt; nine grandchildren, and one great-grandchild.

The family suggests that expressions of sympathy be in the form of contributions to the Wright Institute Graduate School of Social Clinical Psychology in Los Angeles, or the charity of one's choice.