Louis Samuel Rothschild, 84, a retired investment banker who had been a chairman of the old Federal Maritime Board and an undersecretary of commerce in the Eisenhower administration, died of cancer Sept. 1 at his home in Washington.

He came to Washington in March 1953 when he joined the Commerce Department as board chairman of the Inland Waterways Corp. In June 1953, he was appointed to the Federal Maritime Board, and a month later, named board chairman and maritime administrator. From 1955 to 1958, he was undersecretary of Commerce for transportation.

In a 1955 editorial, The Washington Post wrote, "When Mr. Rothschild, a Kansas City department store executive, took over as maritime administrator two years ago, the agency had become little more than a tool of the shipping interests because of its excesses in doling out subsidies. Mr. Rothschild has worked diligently to give maritime affairs an honest and independent administration. There can be more confidence today that when necessary subsidies are granted they are reasonable and based upon ascertainable fact."

During his years at Commerce, he also served on the Commission on Government Security and the National Advisory Committee on Aeronautics, chaired the Air Coordinating Committee, and served as cochairman of a NATO Planning Board for Ocean Shipping.

After leaving the federal government, Mr. Rothschild remained in Washington and directed a variety of business ventures. These had included the Transportation Equities Corp., the Intermediate Credit Corp., and the Standard R. E. Improvement Co. He had recently retired from investment banking.

Mr. Rothschild was born in Leavenworth, Kan., and served in the Navy during World War I. After graduating from Yale University in 1920, he entered the family business, Rothschild & Sons Inc., of Kansas City, Mo., and Oklahoma City. He became was president of the company from the early 1940s to early 1950s. He was active in charitable in civic organizations in Kansas City, and was a past chairman of its planning committee.

Survivors include his wife of 34 years, the former Emily Bettman, of Washington, and a sister, Jane Mayer of Chicago and Aspen, Colo.