THE AIRPLANE WAS IN CRUISE FLIGHT AT AN ALTITUDE OF APPROXIMATELY 200 FT AGL WHEN A LOSS OF ENGINE POWER OCCURRED. THE PILOT STATED THE POWER LOSS WAS SUFFICIENT ENGOUGH TO PREVENT HIM FROM MAINTAINING ALTITUDE A FORCED LANDING WAS MADE IN A MATURE WHEAT FIELD. DURING THE LANDING THE SPRAY BOOM CAUGHT THE WHEAT AND THE AIRPLANE GROUND LOOPED. POST ACCIDENT INSPECTION REVEALED WATER AND DIRT CONTAMINATION IN BOTH THE FUEL STRAINER AND CARBURETOR. THE ENGINE FUNCTIONED NORMALLY WHEN TESTED AFTER THE FUEL SYSTEM WAS CLEANED OUT.