Irish Republican Army gunmen shot to death a Roman Catholic policeman in front of his wife and three children as he arrived at a church to sing in a choir, police said. He was the 11th policeman to die in violence in Northern Ireland in two weeks. A police spokesman said two men attacked Sgt. Hugh McCormac, 40, in Enniskillen, about 70 miles southwest of Belfast. The IRA issued a statement taking responsibility.