America’s long-promised pivot to Asia was finally gathering momentum — new security deals with the Philippines and India, expanded military exercises, and plans with allies to stay ahead of Chinese technology.

But the Middle East, like a vortex, has pulled Washington back in. And for America’s partners in the Indo-Pacific, many of which already worry that the United States is not moving fast enough to counter Beijing, the sudden focus on Gaza — with Pentagon task forces, ramped-up U.S. weapons deliveries to Israel and rushed visits to Middle Eastern capitals — feels like a loss, delaying progress on some of their most critical challenges.

“What concerns us most is the diversion of the U.S. military’s resources from East Asia to Europe, to the Middle East,” Akihisa Nagashima, a lawmaker and former national security adviser in Japan, said at a strategy forum in Sydney, Australia, last week. “We really hope that conflict is completely finished pretty soon.”

American military commanders have said that no equipment has left the Indo-Pacific. And two top cabinet officials, Defense Secretary Lloyd J. Austin III and Secretary of State Antony J. Blinken, will be crisscrossing Asia this week with messages of reassurance, making stops separately or together in India, Japan, South Korea and Indonesia.

Along the way, they most likely will hear a mix of views about Gaza, with India more supportive of Israel, Japan seeking a more balanced approach, and Indonesia, home of the world’s largest Muslim population, increasingly outraged by the thousands of civilians killed in the Israeli invasion that has followed Hamas’ assault on Israel.

But what these countries all share are questions about how Washington’s entanglement with another distant war, on top of Ukraine, will be weighed against the needs of the Indo-Pacific. Many are asking: How many pledges of support to how many nations can the United States — a power stretched thin abroad and politically divided at home — actually handle?

Weapons are one area of common concern. The defense industry in the United States has struggled with shortages of ammunition being provided to both Ukraine and Israel, including 155-millimeter artillery shells. Guided munitions and more complex American systems are also being funneled to both conflicts, even as American partners in the Indo-Pacific wait for weapons deliveries of their own.

Japan, Taiwan and Australia could face delays on military equipment that has been contracted and promised by the United States.

“It’s not just hardware,” said Andrew Nien-Dzu Yang, a former defense minister of Taiwan. “You have to teach or train the people to operate those systems.”

“The concern is that the United States won’t have a more effective and abundant capacity to deter China,” he added.

If the Gaza war drags on, its impacts could change. While an extended conflict could further strain American arsenals, China may learn from it that urban warfare is extraordinarily difficult, perhaps deterring Beijing from following through on threats to take the densely populated island of Taiwan, which it sees as lost territory.

For now, though, Beijing seems to favor continued brinkmanship. Two weeks after Hamas attacked Israel on Oct. 7, a Chinese Coast Guard ship and maritime militia vessel rammed Philippine ships on a resupply mission to the Second Thomas Shoal, a Philippine outpost in a part of the South China Sea that China claims as its own. It was one of the most confrontational encounters between the two countries in more than 20 years of back and forth over the disputed territory.

A few days later, a Chinese fighter jet came within 10 feet of an American B-52 bomber in a nighttime maneuver over the South China Sea that nearly caused a collision — part of what the U.S. military called a “dangerous pattern of coercive and risky operational behavior.”

China’s goal, according to Adm. John C. Aquilino, the U.S. Indo-Pacific commander, is “to force the United States out of the region.” Pentagon officials have stressed that will not happen.

But for skeptics of America’s commitment, wild swings in Washington’s attention are woven into the historical fabric. Vietnam stands out as one example, but so does the era of George W. Bush. On the campaign trail in 2000, he said, “When I am president, China will have no doubts about our power and purpose in the region, about our strong commitment to democratic allies throughout Asia.”

A month after the terrorist attacks of Sept. 11, 2001, he went to Beijing to meet with the Chinese leader at the time, Jiang Zemin. Avoiding all his previous talk of the rising giant as a “strategic competitor,” Mr. Bush emphasized trade and the need to fight terrorism together.

India still recalls the impact of that shift — the war in Afghanistan pushed the United States closer to New Delhi’s archrival, Pakistan. And with Xi Jinping, China’s current leader, expected to meet with President Biden at a summit in San Francisco this month, some Indian commentators have wondered if Washington may again tilt back to the Middle East.

“If you go back to the old trading relationship and the idea of ‘we’re going to work out accommodation in Asia,’ that would affect Taiwan, Japan, India and all our neighbors,” said C. Raja Mohan, a senior fellow at the Asia Society Policy Institute in New Delhi. “But I don’t think we are there yet.”

For some countries, the rekindled conflict over the Palestinian issue has also inflamed old beliefs that the United States is anti-Muslim, or at least too biased toward Israel. After years of watching Washington avoid confronting the often harsh mistreatment of Palestinians by both the Israeli government and extremist Israeli settlers, some no longer trust the United States to be a fair broker.

When Mr. Austin, the defense secretary, gets to Indonesia, he is likely to face an angry public, if not anti-U.S. protests, despite his efforts to advise Israel’s military on how to avoid civilian casualties in Gaza.

“There is significant cynicism toward U.S. calls for Israeli restraint,” said Chong Ja Ian, an associate professor of political science at the National University of Singapore. “In many ways, the Biden administration has a difficult job and has to bear the baggage of past U.S. policy, which makes it all the more important for the administration to get things right and show that it is trying hard to be evenhanded.”

Efforts by Mr. Blinken to meet with Arab leaders and try to broker a pause in the fighting for humanitarian assistance “somewhat tempers the impression that the U.S. is just simply backing Israel regardless of Israeli actions,” Mr. Chong added. And at a meeting of G7 foreign ministers this week in Japan, the grouping of leading democracies joined that call for “humanitarian pauses.”

But for Japan and many other American partners in Asia, the war in Gaza risks disrupting both oil supplies and progress on security. The faster it ends, in their view, the faster the world can get back to what Washington still defines as its most important challenge: deterrence and competition with China in an interdependent world.

Asked in Japan on Wednesday if the United States was too occupied with the conflicts in Gaza and Ukraine to continue its pivot to Asia, Mr. Blinken said: “I can tell you that we are determined and we are, as we would say, running and chewing gum at the same time. The Indo-Pacific is the critical region for our future.”

“Even as we’re dealing with a real crisis in Gaza and the Middle East,” he added, “we’re also not only able, but we’re fully engaged in all of the interests we have in the Indo-Pacific.”

Motoko Rich contributed reporting from Tokyo.