On January 30, 2000, about 1436 hours Pacific standard time, a Siai-Marchetti SF260, N65FD, operated by the owner-pilot, experienced a total loss of engine power during a business flight approaching the Napa Airport, Napa, California. The pilot made a forced landing in a rough field about 300 yards short of runway 18R. During rollout the airplane encountered soft terrain and was substantially damaged. Neither the commercial pilot nor the passenger was injured. Visual meteorological conditions prevailed. An instrument flight rules flight plan had been filed, and was cancelled prior to the accident. The flight was performed under 14 CFR Part 91. The pilot reported that the flight originated from Phoenix, Arizona, about 0920 mountain standard time. The pilot indicated to the National Transportation Safety Board investigator that while en route he monitored the rate of fuel usage for the planned nonstop flight to Napa. He stated that approaching Napa he was aware the airplane was low on fuel. He did not advise the Napa air traffic control personnel of his fuel status. All engine power was suddenly lost while on the base leg of the traffic pattern, about 500 feet above ground level. The pilot additionally indicated that he switched fuel tanks and the engine ran for a couple of seconds before stopping again.