John M. McSweeney; 63, U.S. Ambassador to Bulgaria from 1967 to 1970 and a specialist in Soviet and Eastern European affairs for the Department of State, died of cancer Wednesday at his home is Sarasota, Fla.

Before becoming this country's first ambassador to Bulgaria, Mr. McSweeney served as American minister to the U.S. legation there. He was appointed ambassador when the legation was raised to embassy status in 1967.

Mr. McSweeney, who joined the Foreign Service in 1940, served three tours in Moscow, the last as minister counselor n the early 1960s.

He was director of the State Department's Office of Soviet Union Affairs from 1959 to 1961 and also was a political advisor to the Allied Forces for Southern Europe in Naples, Italy, and to the Strategic Air Command in Omaha, Neb.

Mr. McSweeney also had served at diplomatic posts in Canada, Africa, Egypt and Europe.

Following his retirement in 1973, he was an itnernational affairs consultant.

Mr. McSweeney was born in Boston He earned a bachelor's degree from Brown University in Providence, R.I.

A former Washington resident, he had lived in Sarasota in recent years.

Survivors include his wife, Henrica, and two sons, Brian and Dennis, all of Sarasota, and a sister, Patricia Reed of Pompano Beach, Fla.