Thomas J. O'Connell, 53, counsel to the chairman of the Federal Reserve Board and general counsel of the Federal Open Market Committee, died yesterday at his home in Kensington. He suffered from a heart ailment and diabetes.

Mr. O'Connell joined the Federal Reserve System in 1956 as assistant general counsel. He was one of the principal advisers to the Board. After serving as deputy general counsel and then general counsel, he became counsel to the chairman in 1974 under Arthur F. Burns and continued in that position under G. William Miller.

Mr. O'Connell was born in Denver. He came to Washington as a boy. He was a graduate of the Georgetown University School of Foreign Service and the Georgetown University Law Center.

He served in the South Pacific and China with the U.S. Marine Corps in World War II.

He was a trial attorney in the Justice Department, an assistant U.S. attorney for the District of Columbia and a professor of law at Georgetown University before joining the Federal Reserve System.

Mr. O'Connell was a member of a number of professional organizations, including The Barristers.

He is survived by three sons, Kevin J., of Washington, Stephen T., of Rockville, and Timothy C., of Kensington; three daughters, Anne E., of Bethesda, Christeen L., of Rockville, and Cynthia E., of Kensington, and two brothers, Edward C., of Kensington, and Joseph P., of Bethesda.