UNITED NATIONS: The march towards a peaceful settlement in the Iranian nuclear crisis took an amazing step today when Iran agreed to a Thursday meeting that will bring together the foreign ministers of both the United States and Iran, the highest formal contacts between Iran and the United States since the Islamic Revolution in 1979.

Any potential deal could easily fall apart once the two sides get down to the messy details, such as whether and how much uranium enrichment the Islamic Republic gets to keep. The United States wants to be sure Iran does not have enough enriched uranium to “break out” and build a bomb.

But the signs of a thaw in the decades old standoff between Iran and the United States keep on coming. President Barack Obama may very well meet with new Iranian President Hassan Rohani on the sidelines this week in New York of the United Nations General Assembly, which joins together top representatives of countries worldwide.

The stars do seem to be aligned for progress. Hopes have been dashed in the past but there is a feeling that this time is the best chance, and maybe the last. The election last June of perceived moderate Rouhani as president and his appointment of Foreign Minister Javad Zarif, judged to be Western-friendly, make serious negotiations possible. Rouhani, after all, presided over the suspension of uranium enrichment in Iran as chief nuclear negotiator from 2003-2005. Renewing a suspension is the prime UN demand from Iran. If ever there were a dream team of top Iranian officials, this is it, especially as they replace hardline president Mahmoud Ahmadinejad and his rhetorical excesses denying the Holocaust and accusing the United States of staging the 9/11 attack.

Meanwhile, the real power in Iran, Supreme Leader Ali Khamenei told a group of Revolutionary Guards in Iran earlier this month that the time may have come for the Islamic regime to show “heroic flexibility.”

But, and in the Iranian case the “buts” have so far ruled the day, the devil is in the details. The current US offer on the table calls on Iran to suspend medium-level enrichment, which is closer to weapon-grade for making an atomic bomb than the low-level refinement needed for nuclear reactor fuel. Iran would get only limited sanctions relief for this, according to the US scheme. The Iranians, however, want all sanctions against them lifted, especially ones which have crippled their economy, cutting oil sales by over half and so restricting the Islamic Republic’s ability to do banking abroad. This will be difficult to do since the sanctions were imposed in the United States and in Europe by binding decrees.

A former top US negotiator, Robert Einhorn, said at a panel discussion in Washington earlier this month that “the most productive way ahead is for neither the P5-plus-1 side (the negotiating team of Britain, China, France, Germany, Russia and the United States) or the Iranian side to come to the resumed talks with a fixed proposal.” Nothing can be “chiseled in stone.” Instead, “We should sit down and explore what’s possible.” A member of the Obama administration told me the United States is ready to be flexible. Washington, the official said, would be coming to the talks with different proposals in its pocket, namely various amounts of sanctions relief to match what the Iranians will offer.

Rouhani and Zarif, who will lead the talks for Iran, may be wily enough to strike a deal with which the West can work. Iran’s red line will be to keep enrichment, and have their right to enrich acknowledged, even if the number of centrifuges and stockpiles are reduced and future activities are strictly monitored.

The United States will have to make the huge concession of letting Iran keep enrichment, even though the official American position is still to have “not one centrifuge turning.” This has become untenable as Iran has thousands of centrifuges turning and thousands more installed but not yet spinning.

Michael Adler, a veteran foreign correspondent, is an Iranian expert at the Wilson Center in Washington. He writes often on the Iranian nuclear crisis.