DURING A CROSS COUNTRY FLIGHT FROM MANCHESTER, NEW HAMPSHIRE, TO LACONIA, NEW HAMPSHIRE THE AIRPLANE EXPEREINCED TOTAL POWER FAILURE. THE PASSENGER STATED THAT AS SOON AS THE PILOT DISCONNECTED THE AUTOPILOT, THE ENGINE FAILED. SEVERAL ATTEMPTS TO RESTART THE ENGINE WERE MADE BUT WERE FUTILE. THE PILOT MADE A FORCED LANDING IN LAKE WINNIPESAUKEE, ALTON, NEW HAMPSHIRE. THE PASSENGER STATED THAT SHE AND THE PILOT CLIMBED OUT ON THE WING OF THE AIRPLANE AND MOMENTS LATER ATTEMPTED TO SWIM ASHORE. THE PASSENGER SAID WHEN SHE GOT TO THE SHORE SHE COULD NOT LOCATE THE PILOT. THE AIRPLANE WAS FOUND AND RECOVERED ONE WEEK LATER AND BROUGHT TO A HANGAR IN ALTON, NEW HAMPSHIRE, FOR EXAMINATION. THE PILOT WAS NOT FOUND. POST ACCIDENT EXAMINATION OF THE AIRPLANE REVEALED THERE WAS APPROPRIATE FUEL ON BOARD AND THE FUEL WAS NOT CONTAMINATED. THE ENGINE WAS RESTARTED AND PERFORMED SATISFACTORILY. NO ENGINE OR AIRFRAME ANOMALIES WERE NOTED.