Frank J. Bell, 84, retired chairman of the board of B.F. Saul Co., a Washington mortgage banking and realty firm, died of an aneurism Thursday at Sibley Memorial Hospital.

At the time of his retirement in 1961, he had been with the firm for 47 years. He had started there as a runner, was elected vice president in 1920, president in 1952 and board chairman in 1959.

Mr. Bell also had been a director of the American Security Corp. and a board member of the Mortgage Bankers Association of America. He had been active in the Mortgage Bankers Association of Metropolitan Washington, the Washington Real Estate Board and the Washington Board of Trade.

Born in Washington, he served as an officer with the Army in France in World War I.

A member of St. Albans Episcopal Church, Mr. Bell had served for many years as a vestryman and warden there. He also had been on committees of the Washington Cathedral.

He was a life member of the Columbia Country Club.

He is survived by his wife, Isabelle, of the home in Washington; three children, F. Meade Bell, of Bethesda, David P., and Mary Anne B. Grunwell, both of Potomac; three stepchildren, Hugh Conover, of California, Barbara C. King, of Fairfax, and Robert Conover, of Tampa, Fla; a brother, Edward W., of Orlando, Fla., eight grandchildren and two great-grandchildren. His first wife, Eliza Mason Meade Bell, died in 1958.

The family suggests that expressions of sympathy may be in the form of contributions to the American Cancer Society.