An apparent over fueling of a B747-400 led to a fuel spill during taxi that resulted in an extended delay.

Narrative

Within a minute or so of starting taxi I got a call from the Flight Attendant at door 5R informing me there was fluid leaking from the right wing. I informed the Captain and within another minute we got a call from door 4R as well as station operations reporting the same as the Flight Attendant at 5R. In the cockpit we considered the possibility of the fluid being fuel; de-ice fluid or hydraulic fluid. The Captain stopped the airplane. The CFR equipment had been called before we could request it and a PA was made to the passengers. Ramp informed us that station Maintenance was on their way and would plug into talk to us. The Captain tried a SAT phone call to Maintenance Control several times with no success. He was able to contact Maintenance Control by VHF phone patch but they had no real advice and turned it back to station Maintenance. There was eventually another call to Maintenance Control at the prompting of station Maintenance but Maintenance Control had no additional advice. The leak was eventually confirmed to be fuel coming out of the NACA scoop under the right wing with an estimated rate of two to five gallons a minute. We believed it to be due to over fueling of the #3 main tank and the expansion of the fuel as the wing heated up from the sun hitting it. Maintenance wanted us to transfer fuel out of #3 main tank but we did not have a procedure in the flight manual nor anyway to do it from the cockpit. The decision was made to off-load the passengers. All flight attendants and pilots stayed on the airplane. Eventually Maintenance as well as the CFR fire Captain came up the cockpit through the E/E bay. Maintenance tried to transfer fuel from #3 main tank to the center tank with no success. There was reluctance on the behalf of Local Maintenance to get a fuel tanker out to the airplane to de-fuel the #3 main tank. The Fuel Contractor said they did not have an empty tanker available. The issue of having an empty fuel tanker come to the airplane to de-fuel the #3 main tank was eventually pushed by the CFR Fire Captain. He felt we were at this point an hour and a half into this incident and he had considerable assets tied up with our problem. The fuel transfer did eventually start to work with no apparent change of switches in the cockpit. The fuel flow slowly began to stop. In my opinion; if an empty tanker could have been dispatched early in the incident this could have been cleared up much sooner and we might have been able to get to our destination yet that day; instead of going the next day. Also a contributing factor was the unfamiliarity of Maintenance; by their own admission; with the 747-400. The estimated amount of fuel leaked onto the ramp was estimated at 200 gallons by the CFR Fire Captain.