On November 2, 2000, about 1845 eastern standard time, a Cessna 172N, N4654G, was destroyed during a forced landing and post crash fire in Ridgefield, Connecticut, after takeoff from the Danbury Municipal Airport (DXR), Danbury, Connecticut. The certificated private pilot sustained minor injuries. Night visual meteorological conditions prevailed and no flight plan had been filed for the local flight. The personal flight was conducted under 14 CFR Part 91. In a telephone interview, the pilot stated that she performed a pre-flight inspection of the airplane, and noted that the airplane's fuel tanks were completely filled. Additionally, she stated that she drained fuel from the airplane's three drain sources and the fuel was absent of contamination. She started the engine with the fuel selector positioned to the left wing fuel tank, and switched to the right wing fuel tank just prior to taxi. She performed an engine run-up, which included a check of the carburetor heat system and then taxied to runway 26 for takeoff with the intention of practicing "touch and go" landings. After the engine run-up she switch the fuel selector to the "both" position. The time between the engine run-up and takeoff was "less than 5 minutes." The pilot described the takeoff as "perfectly normal." When the airplane was about 450 feet above the ground she glanced at the engine instruments, which were all in the normal range; however, immediately thereafter the airplane's engine experienced momentary roughness followed by a loss of power. The pilot began performing the loss of engine power emergency checklist and verified that both the mixture and throttle controls were in the full forward position; however, she then needed to use both hands to maintain the airplane's glide attitude and was not able to verify the fuel selector position. The pilot made a left turn and the airplane descend into treetops and initially came to rest about 12 to 15 feet above the ground. The airplane then fell to ground and a post crash fire ensued. The pilot exited the airplane through the front windshield, which was broken during the accident sequence, and the majority of the airplane was consumed in the fire. The pilot reported 560 hours of total flight experience, with 250 hours in make and model. Additionally, she stated that she flew the airplane eight days prior to the accident and did not experience any problems. The airplane's engine also sustained fire damaged. Both magnetos and the ignition harness were destroyed. Additionally, the carburetor was destroyed by impact and fire damage. The engine was retained and forwarded to Textron Lycoming, Williamsport, Pennsylvania, where it was examined under the supervision of a Federal Aviation Administration inspector. A complete teardown of the engine did not reveal any pre-impact mechanical failures. The airplane's fuel selector, which was partially melted, was retained and forwarded to the Safety Board's Materials Laboratory, Washington, DC, for further examination. Examination of the fuel selector revealed its "as received" position was approximately 35-degrees counterclockwise from the "both" tanks position, towards the "left" tank position. A representative from Cessna Aircraft Company stated that the position of the fuel selector as observed after the accident would have resulted in a fuel restriction; however, he noted the effect on engine performance if the valve remained in that position over an extended period of time had never been tested. Review of the Airplane Information Manual, Section 4 - Normal Procedures, Before Takeoff Checklist instructed that the fuel selector valve be placed in the "both" position.