The Wall Street Journal | Laurence Norman and Michael R. Gordon: The leaders of the U.S. and Iran arrived here for the United Nations General Assembly with their red lines clearly drawn. French President Emmanuel Macron came determined to bend them—and engineer the first meeting between U.S. and Iranian leaders since the 1979 Islamic Revolution.

The drama played out behind closed doors and, at times, in front of the cameras.

The meeting between President Trump and Iranian President Hassan Rouhani never happened—though it appeared within reach, Western officials said.

Mr. Trump wanted the meeting, the officials said, seeing it as an opening for negotiations on a comprehensive new accord in which Iran would agree to curb its nuclear and missile work and pledge to curtail what Washington sees as its aggressive regional ambitions.

Mr. Rouhani, under instructions from Iran’s Supreme Leader Ali Khamenei not to negotiate from a position of weakness, stuck by Iran’s precondition for new talks: The U.S. must first lift all sanctions it has implemented on Iran since withdrawing from the 2015 nuclear deal in May 2018.

A number of measures were in play as Mr. Macron sought to bring the two leaders together. Among them was a possible European credit line to Iran, unopposed by the U.S., of some $16 billion, the Western officials said. It would offer a critical lifeline to an Iranian economy in a slump under the pressure of U.S. sanctions.

Western European officials sought a commitment from Iran not to take new steps to develop its nuclear program. In exchange, the U.S. was being pushed to back off new sanctions on Iran.

On Friday, both sides attempted to cast the failure to come together in a politically favorable light.

Back home, Mr. Rouhani said he considered meeting Mr. Trump only when the Europeans suggested the U.S. was prepared to lift all sanctions.

“They had explicitly said that they will remove all sanctions,” Mr. Rouhani said in remarks carried by state TV. “But in the sanctions atmosphere, as the sanctions live on,” he said, Iran would be unwilling to negotiate with the U.S.

Mr. Trump responded on Twitter : “Iran wanted me to lift the sanctions imposed on them in order to meet. I said, of course, NO!” The White House declined to comment further on Friday.

A week ago, it wasn’t even clear the Iranians would come to New York. Mr. Rouhani threatened to stay home after Washington waited until the last moment to give a visa to Iranian Foreign Minister Javad Zarif, who was recently hit by U.S. sanctions.

On Tuesday, as Mr. Trump delivered his speech to the U.N. General Assembly attacking Iran’s leadership but saying that the U.S. had no permanent enemies, a meeting between the two leaders appeared possible.

Mr. Macron lobbied Mr. Rouhani and Mr. Trump, who was just learning that he would face an impeachment inquiry in Congress, not to let the chance slip away. France had been pushing since the summer a temporary truce proposal as a confidence-building step toward broader talks on a longer-term agreement.

U.K. Prime Minister Boris Johnson, who also met with U.S. and Iranian leaders, told Mr. Rouhani on Tuesday that he and Mr. Trump “need to be on the side of the swimming pool and jump at the same time.” Mr. Rouhani stayed poolside.

“There were subtle suggestions from both Washington and Tehran about the prospect of negotiations, but I did not see a shift in either side’s bottom line,” said Henry Rome, Iran analyst at the Eurasia Group. This week’s events suggest that “while neither side is ready to make peace, they are very keen to avoid war,” he said.

There was at least some blurring of Iran’s red lines. Mr. Rouhani acknowledged on Thursday that talks with the U.S. remained possible in coming weeks. He made clear to reporters that Iran would be open to talks that go beyond the nuclear file—including on its regional actions and even, perhaps, its missile program—if the U.S. lifted sanctions. He also laid out a regional peace initiative based around U.S. troops exiting the Middle East.

Mr. Macron struck a positive note Tuesday evening, saying the elements of a broader deal were defined and on the table.

Time for diplomacy could be short. Iran has said it would take new steps away from the nuclear accord in November. By then, Mr. Trump could be absorbed in a bitter impeachment fight while next year’s elections draw ever closer, potentially restricting his space for compromise.

“I think we’re are exactly where we were: high risk of accidental escalation and crisis and no one is really trying to resolve the situation,” said Richard Nephew, a senior fellow at the Brookings Institution who worked on Iran under the Bush and Obama administrations. “They’re all just trying to get that last bit of leverage.”
—Vivian Salama and Sune Engel Rasmussen contributed to this article.