Leonard Crane Rennie, 78, a museum consultant, former government employe and the retired president of his own design company here, died Wednesday at Sibley Memorial Hospital after a heart attack. He maintained homes in Washington and Blue Hill, Maine.

Mr. Rennie was born in Perth, Australia, and came to this country as a teen-ager. He lived in New York City, where he designed streetcars and wrote a radio column for the New York Journal of Commerce before moving to Washington in 1932.

During the 1930s, he worked for the Federal Housing Administration and the Works Progress Administration before becoming graphics chief of the Federal Works Agency. During World War II, he was graphics chief of the War Food. Administration. He also worked with the State Department.

In 1949 he founded Design and Production Incorporated, which arranged graphic exhibits for private companies and government agencies. After selling the Alexandria-based firm and retiring as its president in 1970, he became a consultant to maritime museums in New England and to the Chesapeake Bay Museum in St. Michaels and the Mariner's Museum in Newport News.

A sailor, his other business interests included a boat design and production company.

Survivors include his wife, the former Helen Sewell Johnson, of Blue Hill and Washington; a son, Leonard Jr., of Cheverly; a brother and a sister, both of Australia, and two grandchildren.