LONDON (Reuters) — When three top US officials flew to Europe recently to drum up more backing from NATO allies for the troubled Afghan campaign, the only solid offer was of 200 extra German troops in the quieter north of the country.

At a time of growing concern about NATO's ability to keep the resurgent Taliban at bay, Europe's reluctance to help must have worried the trio — Secretary of State Condoleezza Rice, Defense Secretary Robert Gates and undersecretary of state Nicholas Burns. True, at separate NATO talks in Vilnius last week, France said it was studying a possible deployment to help Canadian troops in the more violent south, and participants said Romania, Poland and Norway signalled they could do more.

Germany, nagged by Gates, softened a longstanding insistence that it cannot exceed a self-imposed limit of 3,500 troops in Afghanistan, and no longer excludes reinforcements this year. It was hardly the crush of support the United States wants or needs, seven years after it ousted the Taliban regime that was sheltering al Qaeda.

And given major allies' reluctance or inability to commit resources, it could be months before help does arrive, leaving Afghanistan in the lurch amid grave concern about its future.

Burns, a seasoned diplomat and former ambassador to NATO, was explicit about the difficulties when he addressed a British policy think-tank earlier this week, after a day of intensive talks on the issue at Britain's Foreign Office.

"The problem for NATO in Afghanistan is that we lack a sufficient number of troops on the ground, we lack equipment — especially helicopters — and that's hurting military efforts to defeat the enemy," he said. "NATO never fought a ground war until the Afghanistan war... NATO's future is so much on the line."

The NATO-led International Security Assistance Force has more than quadrupled in size to 43,000 troops in barely four years, but commanders say some promises of troops and equipment still have not materialised.

"It would be better if countries just said they couldn't do something — rather than saying they can and then not doing it — so at least NATO's military planners knew where they stood," said Col Christopher Langton, a senior fellow at the International Institute for Strategic Studies.

Growing concern about Afghanistan was summed up on Wednesday by Britain's Paddy Ashdown, a former UN envoy to Bosnia who was named, but then withdrew, as "super envoy" to Afghanistan. "Defeat is now a real possibility," he wrote in the Financial Times after listing the problems Afghanistan faces, including "NATO in disarray and widening insecurity".

Underlining this concern, Rice went to Afghanistan with British Foreign Secretary David Miliband. They declared the mission at risk unless more partners stepped up to help.

Britain, with 7,800 troops in Afghanistan and 4,500 in Iraq, is too stretched to provide more troops and equipment, and key partners like Canada and the Netherlands have had too many casualties or have domestic reasons for not doing more.

Pressure is building instead on France and Germany, neither of which has a major ground presence in the south. Both say they made substantial deployments in the first years of the mission — when NATO was present only in the capital Kabul and the north — and that it does not make sense for them to switch focus now.But neither country's leader will want to go empty-handed to a NATO summit in Bucharest in early April and speculation is mounting that they will come armed with new offers of some kind.