Whitney North Seymour Sr., 82, who was president of the American Bar Association from 1953 to 1955 and its chairman in 1960, and who was a champion of civil liberties during his more than half century as a New York lawyer, died of cancer May 21 at St. Luke's Hospital here. He lived in Manhattan.

Mr. Seymour served as president of the American Arbitration Association, the Legal Aid Society and the City Bar Association. In addition to serving as president and chairman of the ABA, he served as chairman of bar committees dealing with the rights of individuals as affected by national security, and was instrumental in the adaption of a uniform code of fair procedures for congressional investigations. In 1958, he was chairman of a bar committee that studied the effect of television coverage on trials.

In addition, he taught law at New York University Law School and Yale University's School of Law and was an official of the Carnegie Endowment for International Peace and of Freedom House.

He had been a partner in the New York City law firm of Simpson, Thacher and Bartlett since 1929. Throughout more than half a century of law practice, he specialized in trial litigation, including appeals work, and was known for his advocacy of civil liberties and antitrust cases.

In the 1930s, Mr. Seymour defended a young black Communist, Angelo Herndon, convicted of violating Georgia's anti-insurrection law, largely because he had Communist literature in his room. Mr. Seymour won an appeal of the conviction in the U.S. Supreme Court in 1937.

He once said, "Availability of justice must not depend on the means or the popularity of litigants. Counsel must be provided for the poor and the unpopular."

He was born in Chicago and was a graduate of the University of Wisconsin and Columbia University Law School. From 1931 to 1933, he served as assistant solicitor general in the Justice Department and later as special assistant attorney general in New York.

His wife, the former Lola Virginia Vickers, died in 1975. Survivors include two sons, Whitney North Seymour Jr., a New York City lawyer, and Thaddeus Seymour, president of Rollins College in Florida; seven grandchildren, and two great-grandchildren.