Justin G. McCarthy, 62, a writer, editor and public affairs spokesman for the United Mine Workers of America for 25 years, died at his home in Arlington Sunday of mitral valve disease, a heart disorder.

Mr. McCarthy came to Washington and joined the UMWA in 1948. He worked with the late John L. Lewis, the union's president, and became editor of the United Mine Workers Journal. He held that position until 1973, when he left the union.

He later was director of communications for the Group Health Association of America and in 1974 became an editor of Custom Tex Inc. a firm that provides editorial services for labor organizations in Washington. From 1975 until his death, he was editor of Press Associates Inc., which provides labor news and editorials to publications around the country.

Mr. McCarthy was born in Chicago. He joined the old Chicago Daily News as a reporter in 1935. He stayed on the newspaper for 13 years as a reporter and editor and then won a Nieman fellowship to Harvard University in 1947. He joined the United Mine Workers the following year.

He was a member of the Society of Nieman Fellows, of the National Press Club, and of Sigma Delta Chi, the professional journalism society. He also was a former director of the National Council on Alcoholism and was chairman of the Washington Area Intergroup Association in 1968. He was a member of the Unitarian Church in Arlington.

Suvivors include his wife, LaVerne Williams McCarthy, of the home in Arlington; their son, Justin Gregory, also of the home; a daughter by a previous marriage, Kathleen Romine, of Houston; two stepchildren, James Fair. of Coco Beach, Fla., and Sandra Carothers, of Andover, Mass., and five grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the National Arthritis Foundation.