On October 14, 1996, at 0940 eastern daylight time, a Mooney M-20F, N6434Q, collided with a fence while attempting a forced landing to a state road near Griffin, Georgia. The personal flight operated under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial damage, and the pilot received minor injuries. The flight departed Peachtree City, Georgia, at 0930. Approximately ten minutes into the flight, and while on a visual approach to runway 32, the engine developed a rough running condition. According to the pilot, he switched the fuel selector from the left main fuel tank to the right main fuel tank, and turned on the fuel boost pump, but flight sustaining engine power was not restored. After surveying his forced landing options, the pilot selected a forced landing area and established an approach. As the airplane touched down, the pilot realized the terrain roughness of his forced landing selection. During the landing roll, the airplane collided with a fence, and came to rest adjacent to a state road. During the field examination of the airframe, fuel samples were collected from both main fuel tanks, and the fuel selector. An additional fuel sample was collected from the fuel tanker at the departure airport that refueled the airplane. The examination of the fuel sample from the left fuel tank disclosed that an abnormal level of contamination was present along with an abnormally cloudy visual appearance. The sample contained sand, rust and small pieces of fuel tank sealant. The right main tank sample was similar to the left tank sample except there was no fuel tank sealant found in this sample. In addition to the debris found in the two main fuel tanks, unidentified organic debris was found in the fuel sample collected at the fuel selector valve. The examination of the fuel injector filter assembly disclosed an abnormally high level of coarse debris contamination. The filter body and fitting were heavily coated with oxide or rust. The filter element contained sand and a very high level of rust. There were no other mechanical problems noted during the examination of the aircraft. The origin and time of the fuel system contamination was not determined.