Leo Thomas McCauley, 83, a retired Irish diplomat who lectured at Georgetown University and was a community service consultant of the City Bank and Trust Co., died at his home in Arlington Tuesday following an apparent heart attack.

Mr. McCauley joined the Irish Free State's foreign service in 1929. He served in Berlin, the Vatican, and then New York, where he was consul general from 1934 to 1946. After three years as assistant secretary in the Department of External Affairs in Dublin, he became, successively, Ireland's ambassador to Spain, Canada and the Vatican. He retired from the last post in 1962 and moved to the Washington area.

He taught history at Georgetown in 1963 and 1964, then worked for the City Bank and Trust Co. from 1965 to 1968.

Mr. McCauley was an honorary citizen of New York City and of Maine. He also was an honorary member of the Friendly Sons of Saint Patrick of the City of New York. He was a Knight Grand Cross of the Order of Queen Isabella of Spain and a Knight Grand Cross of the Order of Pope Pius IX.

Mr. Mc.Cauley was born in London-derry. He was educated at University "college. Dublin, where he took a master's degree in ancient classics, and at the King's Inns, "dublin, where he became a barrister. He entered government service as the private secretary to the minister of finance.

Since moving to Arlington, Mr. McCauley had served a term as president of the Arlington chapter of the American Association of Retired Persons.

Survivors include his wife, the former Georgia Gorman, an American whom he met while serving in New York City, of the home, and a sister, Mary McCauley, of Dublin. CAPTION: Picture, LEO T. McCAULEY