The 800-hour private pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that he departed the airport with 6 gallons of fuel on-board enroute to another airport located approximately 40 miles away, where he was expecting to refuel his single-engine airplane. About 10 miles from the point of departure, while at a cruise altitude of 2,500 feet msl, the engine "coughed", and the pilot elected to turn back towards his departure airport. When the airplane was approximately 2 miles from the airport the engine lost power and the pilot elected to execute a forced landing to an open pasture parallel to the interstate highway. The pilot added that while on short final for the forced landing, the airplane encountered wind shear resulting in a hard landing. The winds at the time of the accident were reported from 300 degrees at 20 knots, gusting to 40 knots.