A Military Confrontations’ Diplomatic Triumph with Uncertain Longevity”

It was so close. Had just one missile or drone gotten through and killed a lot of Israelis, American officials feared, the region could have gone up in flames.

So when Israeli and U.S. forces, with help from Arab allies, managed a near-perfect defense against last weekend’s aerial barrage from Iran, it represented not only an extraordinary military and diplomatic feat but also a major victory for President Biden’s effort to head off escalation of the war in the Middle East.

Mr. Biden and his team hoped that the developments over the weekend could give all three major actors enough to claim victory and walk away. Iran could claim vindication for taking aggressive action in response to the Israeli strike that killed some of its top military officers. Israel showed the world that its military is too formidable to challenge and that Iran is impotent against it. And the United States kept the region from erupting for another day.

It may not work out that way, however. Rather than pocketing the win, such as it was, Israeli officials said on Monday that they would respond — without saying when or exactly how — and Mr. Biden’s advisers were bracing to see what that might entail.

A less-visible cyberattack or a pointed but limited military action might satisfy Israel’s desire to re-establish deterrence without provoking Iran into firing back again. A more extensive and in-their-face attack on Iranian soil, on the other hand, could prompt Tehran to mount a counterattack, and suddenly the conflict could explode into a sustained and increasingly dangerous war.

“This weekend we saw Biden at his best,” said Laura Blumenfeld, a Middle East analyst at the Johns Hopkins School for Advanced International Studies and a former State Department policy adviser. “The U.S.-led aerial display with European and Arab regional partners played like an action movie trailer for a new Middle East air defense alliance.”

But, she added, the reality is that the Israel Defense Forces will inevitably respond. “Turning the other cheek is not in the I.D.F. playbook,” she said. “A simple ‘don’t’ won’t work. Israel’s response is not a question of if, but when and how. You can’t get around Middle East math — one grave, opposite one grave.”

Some hawkish analysts said that Mr. Biden was thinking about it all wrong. His effort to avoid escalation may trigger one instead, they argued, because Iran and other enemies have been emboldened by increasingly public disagreements between Washington and Jerusalem over Israel’s conduct of the war against Hamas in Gaza.

“This perception of separation may have been a factor in Iran taking the unprecedented step of attacking Israel directly,” said Ray Takeyh, a senior fellow at the Council on Foreign Relations.

It was not enough to shoot down Iranian missiles, he added.

“Stopping the attacks after they launch is not the same as deterring them from being launched,” he said. “If Biden’s team once more seeks to carve out a space between itself and Israel, then it will invite further conflict.”

The successful defense of Israel was the result of 10 days of intense diplomacy and military coordination by the Biden administration and years of security relationships built up by multiple administrations throughout the region. After it became clear that Iran was planning to strike Israel for the first time after decades of shadow war, American officials scrambled to activate, for the first time, regional air defense plans that have been in the works for years.

American military officials worked closely with Israeli counterparts to map out a scheme to take down incoming missiles and drones, coordinated with British and French forces in the region, and arranged with Arab allies to provide intelligence and tracking data and permit use of their airspace.

Jordan, which has been highly critical of Israel’s war in Gaza, nonetheless shot down Iranian drones crossing over its territory toward Israel. An American Patriot battery based in Iraq shot down an Iranian ballistic missile crossing through Iraqi airspace.

In some ways, the larger cooperation against Iran is the outgrowth of the changing politics of the region, as exemplified by the Abraham Accords sealed under President Donald J. Trump, through which Arab states like the United Arab Emirates and Bahrain established normal diplomatic relations with Israel for the first time. The Biden administration has been attempting to draw Saudi Arabia into the accords, and while no deal has been reached, the sheikhs in Riyadh have been ready to build ties with Israel in part out of shared animosity toward Iran.

The interception of nearly every one of more than 300 missiles and drones without any fatalities in Israel or even major physical damage felt like validation for those who have worked on erecting a web of security arrangements in the region.

John F. Kirby, a national security spokesman for the White House, called it a “spectacular” success. “That’s the upshot here,” he said at a briefing on Monday. “A stronger Israel, a weaker Iran, a more unified alliance and partners. That was not Iran’s intent when it launched this attack on Saturday night, not even close. Again, they failed. They failed utterly.”

Mr. Kirby disputed speculation that Iran did not really intend to do damage because it telegraphed its coming attack for more than a week, and he denied reports that Tehran had even passed along messages through intermediaries giving details about time and targets. He scoffed at the suggestion that more than 300 missiles and drones amounted to just a face-saving exercise.

“Maybe they want to make it appear like this was some sort of small pinprick of an attack that they never meant to succeed,” he said. “You can’t throw that much metal in the air, which they did, in the time frame in which they did it, and convince anybody realistically that you weren’t trying to cause casualties and that you weren’t trying to cause damage. They absolutely were.”

Mr. Biden himself has said little publicly about the strike. “Together with our partners, we defeated that attack,” he said on Monday in his first public appearance since the strike, a White House meeting with Prime Minister Mohammed Shia al-Sudani of Iraq. “The United States is committed to Israel’s security.”

Mr. Sudani, whose country maintains a fragile balance between the United States and Iran, said he favored efforts to stop “the expansion of the area of conflict, especially the latest development.”

But he also used the opportunity to press Mr. Biden about his support for Israel’s war in Gaza. “We’re actually very eager about stopping this war, which claimed the life of thousands of civilians — women and children,” Mr. Sudani said.

The flare-up with Iran has diverted attention from the Gaza war at the very moment when Mr. Biden had begun turning up the pressure on Prime Minister Benjamin Netanyahu to do more to ease civilian suffering.

Shibley Telhami, a Middle East scholar at the University of Maryland, said Mr. Netanyahu had an interest in prolonging the dispute with Tehran, “both as a distraction from the horrors of Gaza and as a way of changing the subject to an issue where he is more likely to get sympathy in the U.S. and the West.”

Mr. Telhami said the success over the weekend did little to undo “the damage of Biden’s strategic failure” in stopping the crisis in Gaza. “It shouldn’t take our attention away from this bigger strategic failure, whose costs have been immense and still unfolding,” he said.

Still, Natan Sachs, director of the Center for Middle East Policy at the Brookings Institution in Washington, said it was no small matter to avert a larger regional war, at least for now.

“Biden deserves big credit,” he said. At the same time, he added, it may fade fast. “We’re still on the edge because the circumstances are extraordinary and the crisis could escalate any day.”