Andrew Maguire Saul, 79, chairman of B.F. Saul Co., a Washington real estate and mortgage banking firm founded by his father in 1892, died Dec. 10 at Sibley Memorial Hospital after a heart attack. He was stricken at his home in Chevy Chase.

Mr. Saul was a third-generation Washingtonian and a graduate of Georgetown Preparatory School and Georgetown University. He joined the family business in the 1920s, and with the exception of Army service during World War II, he remained with the company until his death.

He was president of B.F. Saul from 1947 to 1952, when he was appointed chairman.

Mr. Saul was a director of the old National Union Fire Insurance Co., a trustee of the Better Business Bureau of Washington and a director of American Security Bank, where he had also been chairman of its executive committee. He had been chairman of the board of Chevy Chase Savings and Loan Association since it was founded in 1969.

Mr. Saul was a director of the St. Vincent de Paul Society and a member of the Knights of St. John and the Shrine of the Most Blessed Sacrament Catholic Church in Chevy Chase.

He was a member of the Metropolitan Club, the Chevy Chase Club, the Alfalfa Club and the Friendly Sons of St. Patrick.

His first wife, the former Ruth Clarke Sheehan, died in 1957.

Survivors include his wife, Louise Hoover Saul of Chevy Chase; two children by his first marriage, Ruth Saul Poljevka of Collingswood, N.J., and B. Francis Saul II of Chevy Chase; three stepchildren, Mary Louise Hoover Kenary of Chevy Chase, George Lanman of McLean and Charles Lanman of Washington; a sister, Rose Saul Zalles of Washington, and 14 grandchildren.