Joseph C. Wilson, the long-serving American diplomat whose clash with the administration of President George W. Bush in 2003 led to the unmasking of his wife at the time, Valerie Plame, as a C.I.A. agent, resulting in accusations that the revelation was political payback, died on Friday at his home in Santa Fe, N.M. He was 69. Ms. Plame said the cause was organ failure.