James Patrick Welsh, 75, a retired special investigator for the Montgomery County State's Attorney's Office and a former U.S. Secret Service agent, died of a pulmonary embolism Saturday at Suburban Hospital in Bethesda.

Mr. Welsh was a Pennsylvania state trooper and served as police chief of Doylestown, Pa., for 12 years before joining the Secret Service here in 1941. He was a Secret Service agent until 1956, when he joined the State's Attorney's Office in Montgomery County, from which he retired in 1970.

He was born in Summit Hill, Pa., and attended Villanova University in Pennsylvania.

During World War II, he served as a chief gunner's mate in the Navy in England.

Mr. Welsh was a national president of the National Campers and Hikers Association in 1968 and 1969. He was a past post commander of American Legion Post 268 in Wheaton and a member of Connecticut Avenue Post 163 of the American Legion, the Veterans of Foreign Wars and the Association of Former Secret Service Agents.

He lived in Derwood, Md., where he had served as a Democratic precinct chairman.

Survivors include his wife, Janet, of Derwood; two sons, Dr. James P. Jr., of Carriere, Miss., and Harry M., of Arlington; three daughters, Mary Mauzy of Gaithersburg, Sally Cowan of Arlington, and Judith, of Derwood; a brother, Harry, of White Sulphur Springs, W.Va., and seven grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the scholarship fund of the Association of Former Agents of the U.S. Secret Service in Washington.