Leonard Kaplan, 59, a senior weapon analyst at the Naval Intelligence Support Center in Suitland, died of a heart attack April 26 at Johns Hopkins University Hospital in Baltimore.

During World War II, he had served in the navy in this country and the Pacific as an explosive ordnance disposal expert.

A civilian employee of Naval Intelligence since 1958, Mr. Kaplan was an internationally known expert on foreign naval torpedoes, mines and guns and was considered the Navy's primary manager for analysis of foreign conventional naval weapons systems.

In recent years, he had served on the economic intelligence committee of the U.S. Intelligence Board, the mine advisory committee of the National Academy of Sciences and the weapons subcommittee of the NATO Naval Intelligence Group.

He wrote many papers, articles and books on underwater naval ordnance and held numerous honors from the Navy Department.

Born in Brooklyn, Mr. Kaplan attended the engineering school of the City College of New York. He later graduated from the Naval War College.

From 1945 until 1958, he was patent draftsman in private commercial industry. He was a Master Mason.

He is survived by his wife, Muriel C., and a daughter, Lynn, both of the home in Kensington; a son, Robert L., also of Kensington; his mother, Sybil Kaplan, of New York City, and a brother, Buddy, of Bronxville, N.Y.