By Paul Reynolds BBC News Online world affairs correspondent

In calling on European members of Nato to increase their defence expenditure, the British Foreign Secretary Jack Straw has added his voice to those who say that Nato is heading nowhere unless it decides on a new role for itself and puts up the money to pay for it.

Mr Straw linked the need for more spending to the war on terrorism and other potential conflicts.

His comments were welcomed by Nato sources. Nato spokesman Mark Laity said: "Nato is very much aware of the gap between the United States and Europe and Canada, and one of the main aims of the summit in Prague next month is to close that gap."

But the prospect of more military spending in Nato raises other questions for those who favour a more "civilian role" for Europe in preventing wars not fighting them.

John Palmer, political director of the European Policy Centre in Brussels, told BBC News Online: "Europeans see as part of the answer to the new threats the creation of a system of world institutions to which even the superpower should be accountable."

The US, Mr Palmer said, was being driven by a "worst case scenario" while Europe "tended to put the emphasis on a global order into which even problematic states could be drawn".

On the offensive

At the Prague meeting, Nato will announce a further expansion to the east, and is supposed to commit itself to spending more and spending better, but critics wonder if Nato isn't just going to go on expanding until it bursts.

Nato members are floundering around, wondering what their role really is in the absence of a threat from the Red Army, which is why Nato was founded after World War II.

A new military role is seen as necessary.

A push is on to develop Nato from a defensive organisation based in Europe to an offensive organisation with a worldwide reach.

German General Klaus Naumann, who headed Nato's Military Committee between 1996 and 1999, wrote a devastatingly critical article in the summer edition of the Nato Review. In it, he stated: "Nato is in urgent need of revitalisation. Its credibility is at stake."

Firepower

Nato officials say that the Americans are now so far ahead of other member states that even the British are "only hanging on with their fingertips".

The only capabilities the Americans would really like of the British during an Iraq war, for example, would be special forces, air-to-air refuelling and minesweeping. The rest would simply be political backing.

Nato, the sources say, has far too many tanks and barracks and planes which don't fire precision-guided weapons.

Europe spends 40% of what the US does but does not get 40% as much firepower.

Robertson's shopping list

And the US is getting impatient. The test will be, they say, whether Nato manages to form the response force called for by the US Defence Secretary Donald Rumsfeld.

"The Americans do want Nato to be worth caring about," said one Nato official.

But without an active European arm, the US will increasingly go it alone.

The Nato Secretary General, George Robertson, has circulated member states with a virtual shopping list urging them to specialise in specific areas. Europe, he feels, cannot do it all but it can do much more.

These include mobile headquarters units, better command, control and computing abilities and a greater ability to deploy forces.