Marvin A. Block, 86, a pioneer in persuading physicians to treat alcoholism as a disease. Block, a retired professor at the State University of New York at Buffalo, lectured and wrote widely on alcohol abuse and addressed medical groups in Europe, Africa and Australia as well as throughout the United States. His 1952 article, "Alcoholism--the Physician's Duty," was acclaimed as one of the two most significant scientific articles published during that year by the American Academy of General Practice. In November, 1953, he was appointed chairman of the American Medical Assn.'s Subcommittee on Alcoholism, designed to educate physicians about the disease and to convince them that alcoholism is an illness they are obliged to treat. After three years of intensive effort, the AMA House of Delegates voted to declare alcoholism "an illness which properly falls within the purview of medical practice" and urged all doctors and hospitals to treat it as such. In Buffalo, N.Y., on Tuesday.