PARIS — French-American relations, often a study in how close love can be to hatred, have taken an interesting turn of late. The cheese-eating surrender monkeys of France, in the phrase from “The Simpsons,” have become the world’s meat-chomping enforcement tigers. As for the United States, it has, in the French view, gone a touch camembert-soft.

The administration of President François Hollande is not known for its decisiveness on the domestic front. Vacillation accompanies economic drift. But, perhaps in compensation, it has shown a resolute streak in international affairs. From Mali to Syria and now Iran, French firmness has been the rule. Paris finds itself to the right of Washington.

This has led to differences. There is talk of the trauma of Aug. 31. On that Saturday afternoon President Hollande took a call from President Obama. A ramped-up France was in a state of readiness for the expected joint military response the next morning to the Syrian regime’s use of chemical weapons. Until Obama let drop his now notorious “non” after he had opted during a walk in the garden for a different course.

France felt ill-used, having stretched to support its ally as Britain faltered, only to find itself dangling in foolish-looking vassal mode. Now, some 10 weeks later, Syria has revealed its chemical weapons arsenal and committed to giving it up. But, in the French view, the last-minute deal has also legitimized President Bashar al-Assad, put a nail in the coffin of the nonradical Syrian opposition and so set back any conceivable resolution of a devastating conflict. The French view is persuasive.

Then along came the Iran nuclear dossier, a subject on which successive French presidents — from Jacques Chirac through Nicolas Sarkozy to Hollande — have had a consistent view: The Islamic Republic wants a bomb; only a tough approach will stop it. Once again the French had the feeling of being presented by the Obama administration with a wobbly fait accompli.

For weeks before the Geneva meeting at which hopes for an accord first soared and then sank, the United States and Iran had opened a quiet two-way negotiation on a six-month interim deal. Officials close to Laurent Fabius, the French foreign minister, told me these bilateral discussions had produced an agreed U.S-Iranian text (with caveats) by the time the Geneva talks opened. When the French saw it they were troubled.

Their concerns focused on three areas: The heavy-water plant at Arak that the Iranians are building, where the outline agreement seemed to allow continued construction; language that appeared to concede prematurely an Iranian “right to enrich” or something close to it; and what measures exactly Iran would take to dispose of its stockpile of 20 percent-enriched uranium. Much of the Geneva meeting focused on the French determination to close these loopholes — only for the changes to prove unacceptable to Mohammad Javad Zarif, Iran’s foreign minister, and his team.

The next few weeks will tell whether France improved the deal or threw it off the rails and lost it. The conviction in Paris is that the accord is still doable. “We did not feel it was smart to rush and we did not feel the original text was balanced,” one official said. “Six months in Arak is a long time. Plutonium is a different issue.” The overall feeling in France observing U.S. actions in the Middle East is of a troubling uncertainty, a retreat that tends to leave a vacuum, a new American determination to work with a “light footprint” that can give the impression of disinterest.

In a speech this week to mark the 40th anniversary of the formation of the French Policy Planning Staff, Fabius dwelt on this perceived trend. “The United States seems no longer to wish to become absorbed by crises that do not align with its new vision of its national interest,” he said, suggesting that this explained “the non-response by strikes to the use of chemical weapons by the Damascus regime, whatever the red lines set a year earlier.” He went on to say this U.S. redirection seemed likely to be “durable,” reflecting the “heavy trauma of the interventions in Iraq and Afghanistan” and the current “rather isolationist tendency” in American public opinion.

Because nobody can take the place of the United States, this disengagement could create “major crises left to themselves,” Fabius said, and “a strategic void could be created in the Middle East,” with widespread perception of “Western indecision” in a world less multipolar than “zero-polar.” The United States, of course, is not quitting the Middle East and isolationist tendencies are easily overstated — as Fabius later conceded.

But his warnings are worth heeding. Obama spoke to Hollande this week; he expressed how “the United States deeply values its relationship with France.” The president could usefully borrow some French toughness to get a winning Iran deal.

When the cheese-eaters are in the White House it is time to worry.