BRUSSELS — For an anniversary bash, the guests are unusually anxious.

The leaders of NATO are traveling to London this week to commemorate the alliance’s 70th birthday — but they will do so at a carefully crafted, foreshortened gathering, not at a full-blown summit meeting.

The low-key celebration seems intended to avoid more awkward comments from President Trump, who nearly blew apart the last summit meeting in Brussels in July 2018, musing about quitting the alliance and walking out in the middle of a statement by Chancellor Angela Merkel of Germany.

Normally, the 70th anniversary, like the 50th, would have been held in Washington, where the alliance’s founding treaty was signed, with three days of pomp, substance and a White House dinner. But given Mr. Trump’s unpredictability and his doubts about the alliance, NATO countries decided to have only a foreign ministers’ meeting in Washington on the actual anniversary, in April.

Despite some misgivings, including from Berlin, this session in London was added because Britain wanted to prove that it still mattered in trans-Atlantic security, particularly with its withdrawal from the European Union looming, said Jonathan Eyal, assistant director of the Royal United Services Institute, a defense research institution based in London.

According to Mr. Eyal, Jens Stoltenberg, NATO’s secretary general, also thought that some event should take place in Europe to mark the occasion.

“There were serious misgivings,” Mr. Eyal said. “After all, at the venerable age of 70, usually one birthday party is sufficient.”

Malcolm Chalmers, a colleague of Mr. Eyal’s at the institute, noted, “This is not a summit, and the amount of time for substantial conversation among the leaders is very short, and deliberately so.” The meeting, he said, has become, “in large measure, an exercise in damage limitation — there is no intention to make any big decisions.”

R. Nicholas Burns, an American former ambassador to NATO, said that originally no one had expected a British election and that “stashing it away in London,” away from Washington, “would help.”

Mr. Trump “has blown up every NATO summit he’s been to,’’ Mr. Burns added, noting that NATO officials and diplomats remained wary of what the American president would say, both in the one morning meeting on Dec. 4 and at his news conference afterward.

Prime Minister Boris Johnson of Britain is also said to be anxious. He is in the last two weeks of a general election campaign, and while Mr. Trump praises him fulsomely, the American president is also widely unpopular in Britain. Any perceived interference by Mr. Trump in the British campaign may hurt Mr. Johnson.

But the NATO meeting has become even more noteworthy because of another outspoken leader, President Emmanuel Macron of France, who recently declared that “what we are currently experiencing is the brain death of NATO.” Mr. Macron also questioned, as Mr. Trump had before him, whether the alliance’s commitment to collective security — Article 5 in its founding treaty of 1949 — remains valid, partly because Mr. Trump, as the leader of the alliance, has questioned it.

Mr. Macron was also angry about Mr. Trump’s side dealings with President Recep Tayyip Erdogan of Turkey, another NATO leader, about pulling American troops out of Syria. French troops are also in Syria fighting alongside the Americans to combat the Islamic State.

Mr. Macron’s comments were sharply criticized by Ms. Merkel and other NATO leaders for undermining the credibility of the alliance, But he has insisted that NATO is spending too much time debating burden-sharing and military spending levels — one of Mr. Trump’s obsessions — and too little time discussing strategy and adaptability in a changing world and battlefield.

So Mr. Macron has made this meeting potentially more substantive, Mr. Eyal said.

“If there was any merit to Macron’s interview, which was disastrous for his own interests, it was to toss a grenade and restart an old debate: Should European security be done in parallel with the United States or instead of the U.S., as a replacement,” he said. “That’s the real dividing line.’’

Ivo Daalder, another American former ambassador to NATO, said that, beyond Mr. Trump’s criticism, the alliance could point to an enhanced deterrence after the Russian annexation of Crimea in 2014. NATO members have increased their military spending by some $130 billion since 2016, according to official figures (though only nine of the 29 members are spending 2 percent of gross domestic product on the military, the alliance’s goal by 2024.)

Mr. Trump has also deployed more American troops and equipment in Europe alongside NATO allies in countries neighboring Russia, such as Poland and the Baltic nations.

“Deterrence is strong and getting stronger,” Mr. Daalder said. But he and Mr. Chalmers, of the Royal United Services Institute, pointed out that spending was not the only measure of deterrence. As Mr. Chalmers put it, “Ultimately, NATO’s credibility depends on perceptions of the political credibility of its leaders, not on the military hardware.”

“That is the legitimate question Macron is raising,” Mr. Chalmers added, even if the French president’s publicly expressed doubts damage the very deterrence he worries about.

Mr. Daalder, now president of the Chicago Council on Global Affairs, sees in Mr. Macron the re-emergence of a Gaullist perspective, “where France is seeking the mantle of European leadership by setting Europe against the United States.” But that may be counterproductive, he added, because it could end up “dividing the Europeans, who are already divided over Brexit and China.’’

Combined with concerns about the leadership in the United States, both before Mr. Trump and after him, Mr. Daalder said, “France is using those doubts as a way to try to establish a strong European defense identity and sovereignty.”

But that feeds into American doubts about European aspirations to “strategic autonomy,” Mr. Daalder added, “and if Europeans do it against NATO instead of in collaboration with it, because ‘we cannot trust the U.S.,’ then you’re back” to the 1960s, when France pulled its troops out of NATO.

Mr. Macron has defended his comments, and some analysts say they believe that this meeting may authorize a lengthy study of NATO’s future strategy, updating the last one in 2010. Drawing that out would kick the whole issue down the road, certainly past the American presidential election in November 2020.

A short final communiqué after the meeting this week is expected to mention the usual spending goals, NATO operations in Afghanistan and elsewhere, the need to work on new disruptive technologies like artificial intelligence and some line of concern about China. It will probably also repeat the usual boilerplate statements on Russia — focusing on deterrence, but stressing readiness for dialogue.

And as a gesture to Mr. Trump, NATO has agreed to cut the American share of the alliance’s $2.5 billion annual budget, beginning in 2021, so that Germany and the United States will both pay around 16 percent. France, however, objected to what is an essentially symbolic gesture to Mr. Trump, and will be the only ally not to pay a little more.

Jean-Claude Juncker, who just left his job as president of the European Commission, spoke for many in Europe when he wrote in Politico recently that “Europe must remain a strong pillar of NATO, which is not so much ‘brain-dead’ as in a light slumber from which it can be easily roused.’’

The challenge for Mr. Stoltenberg is a delicate one, Mr. Daalder said. He must try to “get through this three-hour meeting so that Trump can walk away and say, ‘I won’; to keep Trump happy so the alliance doesn’t fall apart.”

But he also needs to keep Mr. Macron content, too.