BERLIN, Germany — NATO’s first secretary-general, Lord Ismay, famously said the purpose of the alliance was to “keep the Russians out, the Americans in and the Germans down.”

Well, the Germans are well and truly up again and the Russians will drop by for talks with the NATO alliance when it meets this weekend in Lisbon to finalize its new 10-year “Strategic Concept."

That leaves the third challenge, keeping the Americans in — and it is one that is being discussed earnestly in Europe.

“We have to take it very seriously,” Hans-Friedrich von Ploetz, a German diplomat who worked on NATO’s new strategy, told Der Spiegel magazine this week. “Americans are pragmatic … . For Americans, Europe is no longer the central point of reference. In opinion polls, only 20 percent of them hold a positive view of the alliance — a smaller figure than in any other NATO country. Europe has to take this into account.”

The North Atlantic Treaty Organization, by almost universal assessment, is the most successful strategic alliance in history. Set up in 1949 for the collective defense of Europe and the United States against the Soviet Union, its heart and soul, Article 5, guaranteed that an attack on one member was an attack on all.

Even after the Cold War ended, and many questioned its relevance, NATO adapted itself and expanded to incorporate many former eastern European nations.

Now, for the first time since 1999, it is officially updating its strategy — making Lisbon, in the words of Secretary General Anders Fogh Rasmussen “one of the most important summits in NATO’s history.”

But analysts say that while NATO is still useful and reassuring when it comes to European stability, there are serious question marks about what the 28 members actually want from it — particularly the U.S.

While the full details of the new Strategic Concept haven’t yet been released, Rasmussen has already laid out an ambitious program to modernize the alliance by making it better able to cope with new challenges such as terrorism, cyber warfare and threats to energy security, while enabling it to work more closely with outside partners who are not NATO members.

Shortly before the summit began, Rasmussen told Britain's Daily Telegraph newspaper that NATO had to be prepared for expeditionary warfare beyond Afghanistan.

"Our core function will remain territorial defense of our populations," he said. "But we must realize that in the modern world we have to go beyond our borders to actually protect and defend our borders."

“This idea that it’s a historic summit is ridiculous. I don’t see this as anything more than a holding operation for NATO,” said Stephen Szabo, a European affairs expert and executive director of the Transatlantic Academy, a Washington think tank.

“I just came back from China,” he said. “Once you go out there you see that’s where the U.S. is interested … Asia and the Pacific. We’re talking about Australia as a special relationship rather than Britain.”

In fact the security issues in Asia are much more serious, he said.

“Their real challenge is China, not Russia or even Islamic terrorists,” he said. “And you really feel Europe is not really in the game on this.”

This feeling was echoed by Sven Biscop from the Royal Institute for International Relations, a think tank in Brussels. However, NATO might still be a way for the U.S. to steer policy in Europe, he said.

“But at the same time, I feel that NATO has become much less central to U.S. policy," Biscop continued. "If you go to Washington, you'll find easily that NATO is not number one on their list of priorities."

Clara O’Donnell, a research fellow at the Centre for European Reform, said there was “a lot of truth” to German diplomat von Ploetz’s doubts about U.S. enthusiasm.

The United States knows that Europe is still its closest ally, she said. But America might not want to “stay fully engaged with NATO” if it means getting involved in “European neighborhood issues” such as the Balkans, especially if Europe doesn't want to help out on future expeditionary wars like Afghanistan.

“Afghanistan has frustrated a lot of people in Washington about working with the alliance,” O’Donnell said. “They felt they have had to invest a lot of time and energy trying to persuade allies to contribute more troops and the end result from an American perspective is that there are still not enough troops around.”

If the United States were to embark on another war on foreign soil, it might not bother going through NATO for help, she said. The simple fact was that western Europe had little stomach for expeditionary warfare. This makes the ambitious strategy to be outlined in Lisbon all the more implausible, O’Donnell said.

“They need to emphasize that for their own political credibility but that doesn’t mean there is the political appetite for those sorts of operations,” she said.

O'Donnell likened the summit to “a surrealist play” in which everyone was ignoring the growing disparity between NATO’s stated ambitions and the fact that European countries were dramatically slashing their defense budgets because they felt fundamentally safe — the latest terrorism warnings in Germany notwithstanding.

“They will paper over the cracks. But the two things that really need to be addressed are the two things that will be avoided. The first is that everyone has a different view about what NATO is for and the second is that no one has any money and no one wants to invest any resources. Those will be the two elephants in the room.

“The take home message would be: Don’t disband it but don’t use it.”

Ironically, the most conspicuous area where NATO could still be very useful is the one it was originally set up for: dealing with Moscow. Analysts agreed that Russian President Dmitry Medvedev’s presence in Lisbon was a step forward, especially as it is likely to pave the way for a missile defense shield for Europe — something Russia has long opposed because it would weaken its nuclear deterrent.

While there has been some concern in Washington that Germany and France have been too cozy with Russia, the fact is that the European giants and the Obama administration are on the same page when it comes to improving relations with Russia, the Transatlantic Academy’s Szabo said.

“In this respect, the U.S. likes NATO because it keeps them in the game,” he said.

On that score, von Ploetz offered an updated version of Lord Ismay’s quip about the founding purpose of the alliance: “Today, Lord Ismay might have said: ‘We have to include the Russians in the alliance, if only to keep the Americans in.’”