The pilot was en route to the destination airport when the airplane engine lost power, regained power, and then lost power again. The pilot said that he then placed the mixture control in the full rich position, turned on the electric fuel pump, and moved the throttle control, but the engine still did not regain power. The pilot attempted a forced landing on a corn field and the airplane struck two traffic signs on roll out that were adjacent to the field, substantially damaging the wings. The pilot was uninjured. Inspection of the engine revealed no anomalies that would have precluded normal operation.