Mr. Cohn's 38-year career brought him prominence, political influence and personal celebrity but ended in disbarment in New York State. Roy Marcus Cohn, who was born in New York City on Feb. 20, 1927, was the son of Dora Marcus and Albert Cohn, and was brought up in a Park Avenue apartment. His father, a justice in the Appellate Division of State Supreme Court, was a onetime protege of the Tammany boss Ed Flynn and wielded substantial power in the Democratic Party. By age 20 he had breezed through the Fieldston School in the Riverdale section of the Bronx, Columbia College and Columbia Law School. He had to wait until he was 21 to be admitted to the bar, and the day he was admitted, he used his political connections to get on the staff of the United States Attorney in Manhattan. As an assistant United States Attorney specializing in subversive activities, he was soon to come to public attention as a boy wonder. By early 1953, Mr. Cohn's brand of anti-Communism had won him so much admiration from Senator McCarthy, the Wisconsin Republican, who was the chairman of the Senate's permanent investigations subcommittee, that Mr. Cohn was named chief counsel to the subcommittee. This was much to the chagrin of Robert Kennedy, the Democratic minority's counsel, who coveted the job, and was the beginning of an enmity between the two men that was to last for years. the immediate cause of death was "cardio-pulmonary arrest." She said the death certificate also listed two secondary causes of death: "dementia" and "underlying HTLV-3 infections." Most scientists believe the HTLV-3 virus is the cause of AIDS.