Shortly after takeoff, both engines lost power. The pilot said he selected different fuel tanks, but could not restart the engines. He subsequently made a wheels-up forced landing in a field below his flight path. The pilot stated that he had performed a preflight inspection and that there was 4.1 gals in both the front left and right main fuel tanks. Examination of the airplane after the accident revealed a combined total of about 5 gals in the forward left and right tanks.