NATO's challenge: Keep U.S. on board

LONDON, England (CNN) -- Russian foreign ministers and U.S. secretaries of state greet each other these days with handshakes and hugs, not with glowers and grimaces.

But what sort of a NATO is it that decided in Iceland last week to embrace Russia and share discussions on a range of key issues?

Has the United States OK'd that new deal simply because it doesn't much rate NATO any more? And does the same go for NATO's plan to take in another seven or eight new members from the ex-communist world?

The applicant countries recognise their limitations.

"We are very small and we don't really create big unrealistic pictures before us, but rather we are prepared to be a member country of NATO which is specialised on very clear fields," says Estonian Foreign Minister Kristina Ojuland.

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So, if their contributions are small and aims narrow, do they help -- or hurt?

"I don't think enlargement will weaken NATO," says Rear Adm. Richard Cobbold, director of the Royal United Services Institute.

"It might weaken its capability density just a bit, because some nations won't be able to contribute much, especially to out-of-area expeditions that NATO might undertake. But they do have very considerable ability to defend their own countries."

Ten more European countries want to join NATO. They fraternise keenly when they can. But they can't be sure exactly what they'd be joining.

NATO Secretary-General George Robertson says the organisation must modernise or be marginalised. But modernisation costs money.

And to the anger of the United States, other NATO leaders aren't putting their hands in their pockets. Which raises a big question.

"If you go back to the first secretary-general of NATO Lord Ismany's dictum that the purpose of NATO was to keep the Soviets out, the Americans in and the Germans down, it is clear that NATO has changed enormously," says Cobbold.

"The Germans quite rightly are up. The Russians -- now they're taking part in the council and have a special relationship with NATO -- are very much in. I think the great challenge to Europe is to make sure that the U.S. does not go out and stays in and totally engaged."

For the moment a United States which these days fights its wars with coalitions of the willing still welcomes NATO's pool of experience and training to help put those coalitions together.

But if European governments don't come up with hard cash soon to hike their defence spending, some defence experts wonder how long it will be before the United States loses patience with the alliance altogether.