THE AIRCRAFT CRASHED SHORTLY AFTER TAKING OFF FROM THE GREATER WILMINGTON AIRPORT, WILMINGTON, DE. THE PILOT STATED THAT THE LEFT ENGINE LOST POWER AT ABOUT 100 FT AGL, JUST AS THE LANDING GEAR WAS BEING RETRACTED. HE SAID THE AUTOFEATHER WAS ARMED, BUT THE LEFT PROPELLER DID NOT AUTOMATICALLY FEATHER. HE MANUALLY FEATHERED THE LEFT PROPELLER AND CHECKED THAT THE GEAR WAS RETRACTING. THE AIRSPEED DECREASED TO ABOUT 100 KTS. HE STATED THAT HE BEGAN A DESCENT TO ACHIEVE THE BEST SINGLE ENGINE SPEED, BUT LEVEL FLIGHT COULD NOT BE SUSTAINED. REALIZING HE WAS COMMITTED TO A FORCED LANDING, HE CLIMBED TO CROSS OVER A POWER LINE, LOWERED THE GEAR AND FLAPS, THEN LANDED IN AN OPEN FIELD. DURING TOUCHDOWN, THE LEFT GEAR HIT A MOUND OF DIRT AND SEPARATED. WHILE SKIDDING TO A STOP, THE RIGHTMAIN GEAR ALSO FAILED. AN EXTENSIVE INVESTIGATION REVEALED NO REASON FOR THE ENGINE FAILURE.