Lanier Park McLachlen Sr., 91, retired chairman of the board of the McLachlen National Bank who had been active in many civic affairs, died of a cerebral hemorrhage Friday at the Carriage Hill Nursing Home in Bethesda, where he had resided for about a year.

Mr. McLachlen retired from day-to-day banking operations in 1973, but continued to serve the bank as a director and consultant. A former resident of his native Washington and of Chevy Chase, he had lived in recent years in Annapolis.

He started his career in 1909 as a runner for McLachlen National Bank, which had been founded by his father, Archibald Malcolm McLachlen, who was then bank president. He later managed the bank's extensive real estate holdings and became bank president in 1922 upon the death of his father.

He played a key role in moving the bank's headquarters to its present location at 11th and G Streets NW and in sponsoring the "DC Boosters Club" two years later.

Mr. McLachlen had been president of the District of Columbia Bankers Association, the Washington Board of Trade and the Columbia Country Club. He had served as a trustee of Holton Arms School, chairman of the board of Sibley Memorial Hospital, and a member of the Federal City Council. He had been a director of the Rotary Club of Washington.

His wife, the former Evelyn H. Stevens, died in 1975.

Survivors include two sons, Thomas P., of Rockville, and Lanier P. Jr., of Potomac, three grandchildren and one great-grandchild.

The family suggests that expressions of sympathy be in the form of contributions to Holton Arms School or a charity of one's choice.