Mary Chilton Andrews Carlton, a former theatrical agent for the Thelma White Agency, died Oct. 25 of an apparent heart attack at her home in Ventura County. She was 76.In addition to working for Thelma White, Carlton served as theatrical director for the Caroline Leonetti Agency from 1979-81. In 1980, Carlton signed an unknown Kevin Costner to an agency contract. She retired in 1987. She is survived by three daughters and six grandchildren.