WITH the CBS News investigation of Memogate almost done, Mary Mapes, the producer who obtained the fake memos used in Dan Rather's George Bush-bashing report, is fighting to save her job and her reputation. The sleuths at ratherbiased.com report Mapes wrote up a 68-page statement in her own defense and has been lobbying to convince the CBS probers that Rather's exposé on Bush's National Guard service was accurate, even if the documents obtained from a crackpot Texas Democrat were bogus. Rather acted preemptively by quitting as the "Evening News" anchor.