The change of direction comes as Washington swings its weight behind a troop build-up in the Balkans. The deployment of 50,000 troops is intended to serve as the peacekeeping force for Kosovo in the event that the air war succeeds. If it does not, then the same troops will be the core of a possible invasion force.
The proposals were drawn up by General Wesley Clark, Nato's supreme commander and he has won pledges behind the scenes from military chiefs to supply enough troops. It is likely that Britain will increase its commitment to around 10,000 soldiers.
Nato aims to have most of the troops in place by the G8 summit in Cologne. By then, it will also have discussed a possible new plan for land invasion, though there is heavy opposition from within the alliance.
Robin Cook, the Foreign Secretary, is planning a whistle-stop tour of Europe to finalise details of the "road map" for the next few weeks. There is some frustration in Whitehall that other members of Nato - particularly Germany and Italy - have been dragging their feet because of domestic political pressure.
The US Department of Defence has sharply switched tack: for the first time, officials accept that the air war may not succeed in its aims. Though there is no intention to stop the bombing, the White House now accepts that it may be necessary to think about new military options.
The aim is to finish the campaign by the end of September, but efforts are being stepped up to "winterise" refugee camps in Albania and Macedonia.
In another of the intelligence failures that have marked the campaign, Nato admitted yesterday it had struck a former Serb army post which had been occupied by Kosovo Liberation Army guerrillas for a month, on the assumption it was still in Serb hands. Wounded KLA fighters were taken to hospitals in Albania.
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