The pilot had not flown for over 90 days and was practicing landings before flying with passengers. While climbing from a touch-and-go landing, the engine lost power at about 250 to 300 feet above ground level. The pilot saw only a river ahead, so he attempted to turn and land on the airport. He stated that he dropped the nose to maintain airspeed but was unable to keep from hitting trees. The aircraft was destroyed by impact with the trees and ground. The fuel selector was found positioned halfway between the left and right positions. No fuel was found in the fuel strainer or fuel lines forward of the firewall. When the fuel selector was moved to either the left or right positions, fuel flowed freely, but no fuel would flow in the intermediate position. The investigator noted that when the flaps were selected, the fuel selector could easily be bumped. Also, the detents on the selector were weak and the selector could easily be moved. AD 85-05-02, Amendment 39-5912, was not complied with; however, if so, it would not have prevented this problem.