John P. Barnes, 75, a retired general counsel of the Chesapeake & Potomac Telephone Co. who was a member of the Washington Board of Trade and the Washington Urban League, died of cardiopulmonary arrest July 20 at the Lynn House nursing home in Alexandria.

Mr. Barnes, a resident of Chevy Chase, was born in Chicago, where his father, John Barnes, was chief judge of the U.S. District Court. He graduated from Bowdoin College in Brunswick, Me., and earned a law degree at the University of Chicago. He practiced law in Chicago until moving to the Washington area in 1942.

He began his career here with the World War II Office of Price Administration. After the war, he went to work as an attorney for the American Telephone & Telegraph Co. In 1958, he was named general counsel of C&P. He continued that work until his retirement in 1975.

Mr. Barnes was active in politics in Montgomery County. His son, Michael D. Barnes, is a Democrat who represents Maryland's 8th District in the U.S. House of Representatives. Mr. Barnes was his son's campaign treasurer in 1982 and 1984.

The senior Mr. Barnes was a member of the Lawyers Club, the University of Chicago Alumni Association and the Columbia Country Club. He also was a member of the First Church of Christ, Scientist, in Chevy Chase.

In addition to Rep. Barnes, of Kensington, Mr. Barnes' survivors include his wife, Vernon S. Barnes of Chevy Chase; another son, Peter Barnes of Scottsdale, Ariz.; two sisters, Mrs. John Suster of LaGrange, Ill., and Mrs. Stewart Ramsay of Green Lake, Wis., and four grandchildren.