WASHINGTON » Only two weeks after Washington and the nation were debating a unilateral military strike on Syria that was also intended as a forceful warning to Iran about its nuclear program, President Barack Obama finds himself at the opening stages of two unexpected diplomatic initiatives with America’s biggest adversaries in the Middle East, each fraught with opportunity and danger.

Without much warning, diplomacy is suddenly alive again after a decade of debilitating war in the region. After years of increasing tension with Iran, there is talk of finding a way for it to maintain a face-saving capacity to produce a very limited amount of nuclear fuel while allaying fears in the United States and Israel that it could race for a bomb.

Syria, given little room for maneuver, suddenly faces imminent deadlines to account for and surrender its chemical weapons stockpiles — or risk losing the support of its last ally, Russia.

For Obama, it is a shift of fortunes that one senior U.S. diplomat described this week as "head spinning."

In their more honest moments, White House officials concede that they got here the messiest way possible — with a mix of luck in the case of Syria, years of sanctions on Iran and some unpredicted chess moves executed by three players Obama deeply distrusts: President Bashar Assad of Syria, President Vladimir V. Putin of Russia, and Iran’s erratic mullahs. But, the officials say, these are the long-delayed fruits of the administration’s selective use of coercion in a part of the world where that is understood.

"The common thread is that you don’t achieve diplomatic progress in the Middle East without significant pressure," Benjamin J. Rhodes, a deputy national security adviser, said Thursday. "In Syria, it was the serious threat of a military strike, in Iran it was a sanctions regime built up over five years."

To skeptics — and there are plenty in the National Security Council, the Pentagon and America’s intelligence agencies and in Congress — the future is not so rosy. They think Obama runs the risk of being dragged into long negotiations and constant games of hide and seek that, ultimately, will result in little change in the status quo. They argue that the president’s hesitance to pull the trigger on Tomahawk strikes on Syria nearly two weeks ago, and the public and congressional rebellion at the idea of even limited military strikes, was an unmistakable signal to the Syrian and Iranian elites that if diplomacy fails, the chances of military action ordered by the U.S. president is slight.

"These two situations are deeply intertwined," said Dennis Ross, who served as Obama’s lead adviser on Iran for the first three years of his presidency, and who argued for attacking Syria after the Aug. 21 gas attacks that killed more than 1,000 civilians. "If the Syrians are forced to give up their weapons, it will make a difference to the Iranian calculation," and would raise the prospects of some deal with Tehran. "If the Syrians can drag this out and give up just a little, that will send a very different message to the supreme leader."

Hovering over it all is a third negotiation: Secretary of State John Kerry’s effort to jump-start talks between Israel and the Palestinians, a political minefield that Obama and Kerry’s predecessor, Hillary Rodham Clinton, for the most part avoided.

All these possibilities could evaporate quickly; just ask the State Department diplomats who in the last years of the Bush administration thought they were on the way to keeping North Korea from adding to its nuclear arsenal, or the Clinton administration officials who thought they were on the verge of a Middle East peace deal.

Obama will likely know whether the Syrian accord stands a chance of success long before he knows whether the sudden Iranian charm offensive is real or a mirage. The Syrians now face a series of deadlines. The first comes this weekend, when it must issue a declaration of its nuclear stocks that "passes the laugh test," as Gary Samore, Obama’s former top adviser on weapons of mass destruction, put it this week.

The State Department has hinted that the Saturday deadline is not hard and fast. And while Assad will presumably admit to quantities roughly in line with the amounts the United States and Russia have estimated are in his hands, the harder question for the Syrian leader is whether to lead inspectors to every depot, every warehouse, every research and development facility. That is supposed to happen in November, with total disarmament by the middle of next year.

But enforcing that will be difficult. So much time will have passed since the Aug. 21 gas attack that Obama will no longer be able to threaten a strike as punishment for use of the weapons. Instead, he would have to justify any military action as an enforcement of a U.N. resolution he does not yet have in hand, and that is unlikely to authorize the use of force. White House officials say they are not especially concerned: With the world watching and U.N. inspectors on the ground to supervise the elimination of stockpiles, "We would have an effective form of deterrence" against another use of the weapons, Rhodes argued.

Iran is trickier. The coming week will be about symbolism, including the possibility that Obama and newly elected President Hasan Rouhani will arrange to run into each other at the United Nations, where they will both be for the General Assembly. But that would be the easy part. Iranians are desperate for relief from sanctions that have cut their oil revenue by more than half, crashed their currency and made international banking all but impossible, but they may not understand the price of relief. "I suspect they are heading for sticker shock," one official deeply involved in developing the U.S. negotiating strategy said recently.

If rumors prove true, the Iranians may offer to close Fordo, the nuclear facility whose existence was revealed in 2009. The site’s major value to Iran is that it is largely invulnerable to Israeli bombing, but it is so small that it may be more valuable to Rouhani as a bargaining chip.

U.S. officials say they understand that Iran will need some kind of enrichment ability to assure its own people that it has retained its "nuclear rights," as its negotiators say. The question is how much. Unless a good deal of the infrastructure is dismantled, Iran will be able to maintain a threshold nuclear capability – that is, it will be just a few weeks, and a few screwdriver turns, from building a weapon. It is unclear whether Obama can live with that; the Israelis say they cannot.

But the big picture for Obama is that after weeks of appearing uncertain of his way, he now has a chance to pull off something big. "If he gets this right in the ninth inning, no one will remember what the fourth and fifth inning looked like," David Axelrod, Obama’s longtime political strategist, said Thursday. But the president is nowhere near the ninth inning; the game is only now getting interesting.

© 2013 The New York Times Company