NPR documentary producer David Isay last Tuesday won a $500,000 "genius grant" from the John D. and Catherine T. MacArthur Foundation. Isay, 34, is an independent producer, but more than 200 of his "audio profiles" have aired on NPR's All Things Considered and Weekend Edition since October 1988. His works include 1995's Remorse, for which he won Peabody and Robert F. Kennedy awards. In Remorse, two Chicago teen-agers who had taped diaries and interviews with family and friends for Isay's 1993's Ghetto Life 101 interviewed the 10- and 11-year-old killers of a 5-year-old boy. Isay told NPR that his grant, one of 25 awarded yearly, will go into his New York-based production house, the not-for-profit Sound Portrait Productions Inc., to keep doing his radio work.