Marcel Cadieux, 65, a former Canadian ambassador to the United States and to the European Economic Community (EEC), died March 19 while on vacation in Pompano Beach, Fla. He lived in Ottawa.

One of Canada's leading diplomats, Mr. Cadieux became the first French-Canadian to be appointed ambassador to Washington. He represented his country here from 1969 until 1975, when he became Canada's first ambassador to the European Economic Community in Brussels.

In 1977, when the United States and Canada barred each other's fishermen from each country's territorial waters, Mr. Cadieux was appointed a special Canadian negotiator to try to settle the dispute between the two countries.

The following year, he also became an adviser to the Commissioner of the Royal Canadian Mounted Police. He retired last year.

Mr. Cadieux was born in Montreal on June 17, 1915. He graduated from Grasset College in Montreal and earned a law degree from the University of Montreal.

After joining Canada's Department of External Affairs in 1941, he was assigned to London, Brussels and Paris and served as a senior adviser to the International Supervisory Commission in Indochina. He was under secretary of state for external affairs from 1964 to 1969.

Mr. Cadieux's honors included his appointment as a Companion of the Order of Canada.

Survivors include his wife, Anita, of Ottawa, and two sons, Rene and Francois.