The airplane experienced a total loss of engine power on approach for landing at about 1352 Pacific time. The pilot made a forced landing on a soft dirt field, and the airplane came to rest about 500 feet short of the runway. During rollout, the airplane collided with a fence, bending the right wing and lift strut. The airplane was substantially damaged, but the pilot was not injured. Visual conditions prevailed. The pilot subsequently reported the engine suddenly started running rough while cruising about 3000 feet msl. Engine speed rapidly decreased from 2100 to 1900 rpm and the pilot immediately applied full carburetor heat. The engine continued running rough, so he headed toward the nearest airport. While on base leg to land, all engine power was lost, and the pilot observed that he would not be able to glide all the way to the runway.