Anxiety is growing in European capitals and Washington that the US peace plan for former Yugoslavia may fall apart because Nato will be unable to deploy the 60,000-strong force needed to implement the deal.
The political, diplomatic and practical challenges presented by such an operation could well prove too tough for the alliance leaders to surmount, said senior US and European diplomats. "The chances of sending the peace-enforcement force are now only 50-50," one senior British source said.
As world leaders meet at the United Nations this week, there is an acute awareness that if the Nato plan falls apart the consequences could be profound. "Without the peace enforcement force there would be no peace deal and no peace in the former Yugoslavia," a senior US diplomat said. The future of Nato would be called into question if it failed to seize this chance to build a Balkans peace. The West's relations with Russia would also be in danger of deteriorating. "This is a defining moment for Nato; for relations with Moscow and peace in the Balkans. It is going to be very difficult," said a defence planning source.
The most serious threat lies in the reluctance of the US Congress to give President Bill Clinton backing to send US troops with the Nato force. Republicans have always argued that the Balkans is a European, not an American, problem and are desperately afraid of US troops sinking into the quagmire of another foreign conflict. It is, however, inconceivable that the peace plan launched by the US should be implemented without the help of US forces.
Last week the Clinton administration, which clearly sees peace in Bosnia as providing a dream ticket for the 1996 presidential election, began an intensive sales pitch to Congress, presenting the peace-enforcement operation as a chance for the US to show it is the only superpower. In a televised debate on CNN, Warren Christopher, the US Secretary of State, made clear to Americans that this was "no Vietnam" and warned that the stakes for world security were high. If the plan failed, "it will be very hard to predict Nato's future", he said.
"It would be a huge blow if after all this preparation, the Americans found for domestic reasons they can't do it," said a senior European Union source.
The plan is also seriously threatened by the failure so far to agree how Russian forces will be deployed alongside Nato troops. President Boris Yeltsin told the UN yesterday that the Security Council must not be "relegated to the sidelines of events".
It was "inadmissible for a regional organisation [Nato] to make decisions on the mass use of force, bypassing the Security Council," he said. Mr Yeltsin insists Russian forces should be included in the force, and Nato also supports the principle of a Russian contingent. However, the US insists that the force should come under sole Nato command, while Moscow is adamant that the command should be shared with Russia.
Any suggestion that the Russians should share command and control is dismissed by Nato and any Russian control would make it impossible for Mr Clinton to sell the plan to Congress. Mr Christopher admitted yesterday that it would "take some ingenuity" to find a way through the impasse.
Ideas have been canvassed for a special co-ordination committee to give the Russians some low-key say in the decision-making.
Nato says Russians could be given a non-combat role in the force, working with transport, mine-clearance or refugees. However, European intelligence experts put the chances of a deal with the Russians at less than 50 per cent. If the Russians were excluded, the force could still go ahead, but the diplomatic implications could be highly damaging.
Moscow might block votes in the UN security council, and European officials say Russia's exclusion might just "tip the balance" towards a more confrontational attitude from Moscow towards the West. Moscow's relations with Nato are already soured by Nato's plans to expand to the East.
Divisions are also opening up between the US military chiefs and the Europeans over the operational rules for the force.