William H. Leachman Sr., 82, chairman of the board of Johnson & Wimsatt Inc., a wholesale lumber supplier with offices in Alexandria died Thursday at Sibley Memorial Hospital. He had cancer.

Mr. Leachman, who had lived in Washington since 1936, spent more than 60 years in the lumber business. He also was a bank director, a farmer, a member of the board of visitors of Hampden-Sydney College and a Democrat.

He was born in Manassas and grew up there. He began his career in lumber at the age of 20 as a sales representative for Mixer & Co. of Buffalo. In 1937, he joined Johnson & Wimsatt as general manager. He was named president in 1940 and became majority stockholder in 1955. He also was president of two subsidiaries, the White Pine Lumber Co. of Reno, Nev., and the Ashland Lumber Co., of Ashland, Va.

Under Mr. Leachman's guidance, the company opened outlets in Camden, N.J., Georgetown, Del., Newport News, Va., and Raleigh and Greensboro, N.C. It became one of the largest wholesale lumber businesses on the East Coast.

The firm was located in Southwest Washington until 1958, when it moved to Springfield, Va., as the result of urban renewal projects in its old neighborhood.

In 1968, it merged with Boise Cascade forest products company and Mr. Leachman retired.

In the early 1970s, when Boise Cascade began to phase out the old Johnson & Wimsatt operations, John P. Leachman, one of Mr. Leachman's sons, reactivated the company's name and continued in the lumber business. Its offices now are in Alexandria. The senior Mr. Leachman was named chairman when the family resumed control over the firm and he held that position until his death.

He also was a director of the Alexandria National Bank and the old Metropolitan National Bank of Washington. He had farm holdings in Virginia, Maryland, West Virginia and North Carolina.

Mr. Leachman became a member of the board of visitors of Hampden-Sydney about 1970 and was chairman of its executive committee. He was active in Democratic Party affairs in Virginia.

He also was a Mason and a member of St. Alban's Episcopal Church in Washington and the Leed's Episcopal Church in Markham, Va. He was a member of the Chatterbox Club in Washington and the Commonwealth Club in Richmond.

In addition to John P. Leachman of Washington, Mr. Leachman's survivors include his wife, Beatrice L., also of Washington; two daughters, Molly L. Green of Winnetka, Ill., and Nancy L. Friant of Berryville, Va.; another son, T. Keith Leachman of Ashland, Va.; 18 grandchildren and five great-grandchildren. Another son, William H. Jr., died in 1976.

The family suggests that expressions of sympathy be in the form of contributions to the Leed's Church, Markham, Va., or to the American Cancer Society.