But in the past few days, American officials have raised new questions and doubts about these European plans, expressing concerns that they could weaken the NATO alliance and cut out United States military manufacturers from bidding on certain European projects.
Last week, the American ambassador to NATO, Kay Bailey Hutchison, warned that Washington did not want Pesco or a new European Defense Fund “to be a protectionist vehicle for E.U.”
“We’re going to watch carefully, because if that becomes the case, then it could splinter the strong security alliance that we have,” she added, referring to NATO.
A top aide to Defense Secretary Jim Mattis, Katie Wheelbarger, the principal deputy assistant secretary for international security affairs, said that fitting Pesco and NATO together was a key part of Mr. Mattis’s conversations in Brussels with defense ministers last week.
“We are supportive of it, as long as it is complementary to and not distracting from NATO’s activities and requirements,” Ms. Wheelbarger said. “We don’t want to see E.U. efforts pulling requirements or forces away from NATO and into the E.U.”
In his comments in Munich, the NATO secretary general, Jens Stoltenberg, emphasized those same American concerns.
While applauding the new European Union initiative, he said, “I also highlight that we need to avoid duplication” between the Europeans and NATO.
“This is not about an alternative to NATO,” he said, “this is about strengthening the European pillar within NATO.”
“It’s important for Europeans to state again and again that this is not competition for NATO or an alternative to NATO,” he added. “Some doubts remain.”
When pressed, Mr. Stoltenberg said that European efforts must be coherent with NATO goals for equipment needed to enhance capability, European assets must be available for NATO operations and not reserved for particular European ones, and there should be “the strongest possible synchronization” with NATO members who are not members of the bloc, “because the E.U. cannot defend Europe by itself.”
NATO members that are closer to Russia, like Poland, have also expressed concerns that a European Union defense initiative could pull resources away from NATO toward other missions, like France’s expeditions against jihadists in North Africa.
One senior NATO official, who insisted on anonymity because he is not authorized to speak on the issue publicly, expressed confusion and puzzlement over the sudden shift. The official said these random comments, as he described them, reflected a lack of understanding by the White House of the European project, and he put them down to Mr. Trump’s long-held belief that America’s allies take advantage of the United States on trade.
The American concerns seemed exaggerated, the official said, noting that the European Defense Fund represents less than 1 percent of the bloc’s budget and less than 1 percent of member nations’ current military spending.
Daniel Flott, a defense expert with the European Union Institute for Security Studies, a research group, said that he was “surprised to hear the return to the language of duplication, which we thought we had put behind us.” Looking at the early projects for Pesco, he said he saw no duplication with NATO’s.
R. Nicholas Burns, a former American ambassador to NATO now at Harvard, said, “It is a mistake for the U.S. to make this an issue.”
The real task is getting Europeans to spend more efficiently and usefully on defense, he said, given the threats from Russia. “But the E.U. is incapable of creating a competitive structure to NATO,” he added.
This conference of trans-Atlantic security experts is the best place for Washington to reassure European allies and send them messages, as Vice President Mike Pence did last year, asserting Mr. Trump’s support for NATO and the principle of collective defense, analysts say.
But this year, only Mr. Trump’s national security adviser, Lt. Gen. H.R. McMaster, spoke for the administration, and he said little about Europe. Mr. Mattis and the C.I.A. director, Mike Pompeo, did not speak publicly at all.
For many years, long before Mr. Trump’s election, the United States pushed European nations to spend more on defense and to take more responsibility for European security. Mr. Trump has ratcheted up the public pressure, and NATO members are now spending more in real terms. By 2024, NATO says, at least 15 of its 29 member nations are expected to hit the collective goal of spending at least 2 percent of their gross domestic product on defense.
That would be short of the goal of all members spending 2 percent, but it represents significant progress, especially if the money is spent more efficiently and cooperatively.
To that end, the Obama administration had urged Europe to take more responsibility for itself, with the former assistant secretary of state for European and Eurasian affairs, Victoria Nuland, saying that the problem was not a strong Europe but a weak one.
But now, said Ivo Daalder, another former American ambassador to NATO, who now directs the Chicago Council on Global Affairs, the United States is going back to the language of the late 1990s, after Britain and France began a formal defense cooperation. Washington and the Secretary of State at the time, Madeleine Albright, had warned of the “three D’s” — the dangers of “delinking” European efforts from NATO, “duplicating” existing efforts, and “discriminating” against nations that are not members of the European Union.
Mr. Daalder said that the failure to deliver a clear American message of support for Europe was a mistake. The United States should have welcomed the European initiative and increased spending as “a plus for burden sharing” instead of creating friction, he said.
“But President Trump and his administration have made it clear that they see a world of competitors, not allies,” Mr. Daalder said. “They have made it clear they don’t want a strong Europe, but see Europe as a competitor, which can only please Russia.”
The traditional strength of the United States is that it has allies, Mr. Daalder said, “while Russia and China have clients.”