Civil servants are meeting with their American counterparts to work out how to split the massive costs of what is expected to be the most expensive and longest-running criminal case in British legal history.
It would be the first time a foreign power partly financed a court case under the jurisdiction of a British court.
Estimates of total costs range from pounds 50m to pounds 100m. If the two accused, Abdel Basset Ali al-Megrahi and al-Amin Khalifa Fhimah, are convicted and subsequently appeal, court proceedings could last three years.
Last October, President Clinton set aside $8m (pounds 5m) towards building a high-security court at the former Kamp van Zeist airbase in the Netherlands, where the trial would take place. Until now, it was thought that would be the total US contribution. But behind the scenes, pressure is being applied for the Americans to pay an equal share of the costs.
There were 189 Americans among the 259 passengers killed after Pan Am Flight 103 blew up above Lockerbie, in the south of Scotland, on 21 December, 1988. Another 11 people were killed by debris which fell on the town.
A Foreign Office spokesman said: "During the talks the Americans have told us the $8m is not a final contribution. The rest will be determined as discussions continue."
But another Foreign Office source said: "The idea is for an even split." While the negotiations are at what was described as a "sub-ministerial level", they are understood to have government blessing.
A Scottish Office spokesman said: "I am not in a position to talk about figures, but we are speaking to the Americans about all the costs which would be incurred by this unique trial."
The plea to the US followed a debate between government departments over how to divide the bill between the Scottish courts budget and UK coffers.
Last year's budget for the Crown Office, which co-ordinates Scottish prosecutions, was pounds 45m, far less than the likely trial bill. But the Secretary of State for Scotland, Donald Dewar, is said to be "extremely pleased" with a commitment made by the Treasury to foot most of Britain's expenditure.
The bill could include several million pounds of legal aid for the accused men's defence. Legal experts have confirmed they are eligible.
Last August, Libya agreed to hand the suspects over for a trial in The Hague under Scottish law. In the past few days, Colonel Gaddafi has been in Egypt discussing obstacles to handing over the suspects.
The man who drew up plans last year for the trial in a neutral country, Lockerbie-born Professor Robert Black, an Edinburgh University law lecturer, said he doubted the evidence available to the prosecution would lead to a conviction.