But forces have been put in place in a piecemeal, unco-ordinated fashion, and they are not necessarily those that will be needed in the future.
A fully fledged invasion still seems very unlikely. But there are other eventualities for which planning must be made: a peacekeeping force if a deal emerges; a "pacification" force if Serbian control of Kosovo disintegrates; and a holding force if the conflict continues over the winter. There are at least three forces in the Balkans available for operations against Serbia already. In Macedonia there is the core of a Nato peacekeeping force for Kosovo - about 16,000 troops. Albania hosts about 7,000 troops under Nato command, mainly there to provide humanitarian support for refugees. It also has the 5,000 strong American Task Force Hawk, which is built around the much-vaunted but luckless Apache helicopters.
There are various other US formations in the region, including a 2,000- man Marine Expeditionary Unit; and there are several hundred special forces from the US, Britain and France. So in total, there may be 31,000 troops.
But it is hard to quantify these forces because Nato, and especially Washington, has deliberately made the deployment opaque. The US has never made it clear what the Marines are doing, and has bumped up Task Force Hawk twice since its initial decision to deploy. Despite protestations about not planning for a ground war, Hawk is led by a three-star general, which means it could quickly be converted into a corps-size operation.
Other national detachments have taken place in staggered deployments. The result is an increasingly large but rag-tag series of forces reflecting the changing political thinking in Nato capitals, not the military task at hand - which remains undefined. "It's piecemeal," says analyst Matthew Baker at security consultants Stratfor. "It's what they've been able to pick up."
Elsewhere are more forces that could be quickly added. France has 2,000 troops with tanks on standby at Marseilles; the US has a 4,000-strong Southern European Task Force in Vicenza. Then there is the 30,000 strong Nato-led peacekeeping force in Bosnia. S-For has 2,000 Italians, including the elite parachute brigade Folgore; 5,000 British, 3,300 French and 8,000 Americans.
How many soldiers do they need? The peacekeeping force was originally intended to be 28,000 strong, but the consensus seems to be this is no longer enough: 50,000 troops will be necessary, plus those needed in neighbouring countries.
Creating that force from the current position will pose big problems. "Not a lot of full multi-purpose units" are involved at the moment, says Mr Baker. "You would hardly recognise what you started with," says Major General Edward Atkeson of the Institute of Land Warfare. Many of the existing forces could not participate in conflict or would be needed where they are, for logistical and humanitarian work.
There would need to be far more engineers to help resettle the refugees and reconstruct the damage done both by Serb forces and the allied air bombardment. They would need more tanks, and the light infantry component would also have to be increased.
Any new force could be built around Nato's British-led Rapid Reaction Corps or - more likely - Task Force Hawk. It is likely to have a larger US presence - perhaps 15,000, compared to the 4,000 originally foreseen.
Given the lead time, it will take at least two months to move in forces. That means that if they are to be in place before winter starts setting in, the alliance will have to get into gear and start shifting men and machines into the region this month. The creeping deployment will have to come into the open.Reuse content