John B. Cotter, 76, a retired assistant professor of mechanical engineering at Catholic University, died at Providence Hospital Nov. 20 after a heart attack.

Mr. Cotter, who lived in West Hyattsville, was born in Orono, Maine. He graduated from the University of Maine and moved here in 1937 to begin his career at Catholic University. He retired in 1971.

For many years he was a part-time contracting engineer with the Washington Suburban Sanitary Commission. When he left the university, he went to work for the commission full time until 1978, when he retired a second time.

In 1964, Mr. Cotter received the Benemerenti Medal from Pope Paul VI for his services to the university and the Catholic Church. In 1966, he was named the outstanding faculty member of the university's School of Engineering and Architecture. He also was a member of Tau Beta Pi, an honorary engineering society.

Mr. Cotter sang in the choir at St. Mark's Catholic Church in West Hyattsville.

Survivors include his wife, Mary, of West Hyattsville; three sons, John B. Jr., of Silver Spring, Michael, of Riverdale, and Dennis, of Aurora, Ill.; a brother, Robert, of Portland, Maine; four sisters, Virginia Pasco, Marguerite Diggins and Madeleine Kaczmarski, all of Portland, and Alice Collette of Mesa, Ariz., and three grandchildren.