The pilot reported that shortly after takeoff on a parachute jumping flt the left engine lost power, but a second later power was restored. Soon afterwards a total power loss occurred. According to the pilot, the propeller stopped rotating and did not windmill. He did not feather the left propeller. He made a shallow left turn toward an open field, while trying to return to the airport. He was unable to maintain adequate airspeed or altitude, and in order to maintain aircraft control, he reduced power on the right enggine. He made a forced landing in a wheat field. The airplane came to a stop and all occupants escaped the airplane before it caught fire. The examination of the airplane did not disclose evidence of mechanical malfunction.