The pilot stated he had an uneventful cross-country flight and on the downwind leg of the destination airport traffic pattern, he switched the fuel selector from the right tank to the left tank and turned on the boost pump. While on short final approach, the engine started losing power as the airplane was approximately 75 feet above ground level. The airplane subsequently impacted terrain about 600 feet short of the runway and came to rest upright. The pilot further stated that at the time of the engine power loss, he pushed all the controls, mixture, propeller, and throttle full forward and the engine rpm started to increase, but then quickly decreased again. The pilot then shut-off the master switch and walked to the fixed based operator to get help. He then walked back to the airplane, shut the ignition off and took his keys and headset out of the airplane. The pilot added that he did not touch the fuel selector. Examination of the wreckage by a Federal Aviation Administration inspector revealed damage to the wings, landing gear, and stabilator. The inspector also noted that although adequate fuel remained in both fuel tanks, the airplane fuel selector was in the "off" position. The pilot further reported that there were no preimpact mechanical malfunctions with the airplane.