SHORTLY AFTER TAKEOFF AT AN ALTITUDE OF 200 FT AGL, A LOSS OF ENGINE POWER OCCURRED. THE PILOT JETTISONED THE CHEMICAL LOAD AND ATTEMPTED TO LAND IN AN ORCHARD, THEN MANEUVERED THE AIRPLANE TO AVOID A RESIDENTIAL AREA. HOWEVER, WHILE BEING MANEUVERED, THE AIRPLANE CONTACTED POWER LINES AND TREES. SUBSEQUENTLY, IT WAS DESTROYED BY POST-IMPACT FIRE. A TEARDOWN OF THE ENGINE FAILED TO REVEAL THE CAUSE OF THE POWER LOSS.