Retired Army Brig. Gen. john F. Davis, 86, who helped train armored units before World War II and commanded reserve units in Washington after the war, died of pneumonia Monday at the Fernwood nursing home in Bethesda.

Gen. Davis was a native of South Carolina. He was a 1915 graduate of the U.S. Military Academy at West Point.

He served with the cavalry on the Mexican border and in Europe during World War I. Prior to World War II, he was stationed at Fort Knox, KY., where he helped convert horse cavalry to armored units.

He later served on Gen. Douglas MacArthur's staff in the Pacific during World War II and then in Japan during the late 1940s.

He was commanding officer of the District of Columbia Military District reserve components for three years before retiring from the Army in 1952. Among his decorations were the Legion of Merit and the Distinguished Service Medal.

He is survived by two sons, both retired Army colonels, John F. Jr., and William D., both of Potomac, and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Army Distaff Foundation or to St. David's Episcopal Church, Washington.