Mr. Araud, 62, the first openly gay French ambassador to Washington and quintessentially French down to his (sterling silver) cuff links, relishes showing off his country’s cuisine and culture at parties that bring together the city’s top politicians, academics, business leaders, artists and writers. But he is the antithesis of a buttoned-up diplomat issuing scripted statements of harmony.

Instead he is known as an effective and sometimes combative advocate for France.

“He’s a very talented, intelligent ambassador who serves his country well, but he knows how to throw an elbow,” an Obama administration official said, speaking on the condition of anonymity to talk candidly about Mr. Araud. “On occasion, that has caused brief moments of friction.”

He can be a strong negotiator, as was the case during intensive talks earlier this year between Iran and six world powers, including the United States and France, on a deal to lift sanctions on Tehran in exchange for curbing its nuclear program. Mr. Araud criticized the emerging agreement, suggesting it was not tough enough, and publicly questioned whether a deadline at the end of June for striking it was binding. His words undercut what American negotiators regarded as critical leverage at the most sensitive of moments.

“That was directly contrary to what we wanted to do, and it was unhelpful,” said Philip Gordon, who until March was the top Middle East official at the National Security Council. But in an era when the United States and France have mostly common interests and have been aligned on strategic issues, he added, the bluntness can also be an asset.

“He is refreshingly candid, and I stress ‘refreshing,’ because often diplomats can be quite cautious and ultra-diplomatic,” Mr. Gordon said. “I don’t think anyone would say that about Gérard.”