POST WORLD EXCLUSIVE WASHINGTON — Billionaire Marc Rich has emerged as a central figure in the U.N. oil-for-food scandal and is under investigation for brokering deals in which scores of international politicians and businessmen cashed in on sweetheart oil deals with Saddam Hussein, The Post has learned. Rich, the fugitive Swiss-based commodities trader who received a controversial pardon from President Bill Clinton in January 2001, is a primary target of criminal probes under way in the U.S. attorney's office in New York and by Manhattan District Attorney Robert Morgenthau, sources said. "We think he was a major player in this...