WASHINGTON - President Barack Obama arrives at the United Nations today with diplomatic openings, the result of help from unexpected partners, on three fronts: Iran, Syria, and elusive peace between Israel and the Palestinians.

All three pathways are fraught with potential pitfalls and hinge on cooperation from often unreliable nations. Obama also risks being branded as naive and misguided if the efforts fail, particularly in Syria, where he's used the prospect of diplomacy to put off a military strike in retaliation for a chemical weapons attack.

Still, the recent developments mark a significant shift on a trio of issues that have long proved problematic for Obama at the United Nations. His former Iranian counterpart used the annual U.N. General Assembly meetings, which open today, as a venue for fiery, anti-American speeches. Failed Middle East peace talks led the Palestinians to seek statehood recognition at the U.N. despite staunch American objections. And the Obama administration has been stymied on Syria at the U.N. Security Council due to intractable Russian opposition.

But this year, Iran has a new leader who is making friendly overtures toward Obama, raising the prospect of a meeting at the United Nations. U.S.-brokered peace talks between the Israelis and Palestinians have resumed - though on an uncertain course. And Russia has joined with the U.S. on a diplomatic deal to strip Syria of its chemical weapons.

Joel Rubin, a former State Department official who now works at the nonproliferation organization Ploughshares, said the confluence of events underscores an often frustrating aspect of diplomacy.

"You never know when it's going to break," said Rubin. He said Obama's biggest test now is to recognize if opportunities morph into stalling tactics.

Obama's advisers cast the sudden signs of progress as an outgrowth of the president's long-standing preference for resolving disputes through diplomacy and, in the case of Iran and Syria, with pressure built up through economic sanctions and the threat of military action.

"He said we'd be open to diplomacy, we'd pursue engagement, but that there would be pressure if Iran failed to take that opportunity," said Ben Rhodes, Obama's deputy national security adviser. And on Syria, Rhodes said it was the credible threat of a U.S. military strike "that opened the door for this diplomacy."

Aides say Obama will address developments on Iran, Syria and Middle East peace in his speech to the U.N. on Tuesday. The issues will also be at the forefront of some of the president's bilateral meetings with world leaders, including a sit-down with Palestinian Authority President Mahmoud Abbas and Lebanese President Michel Suleiman, whose country is burdened by the flow of refugees from neighboring Syria.

But Obama's most closely watched meeting may end up being with Iranian President Hasan Rouhani. No encounter is scheduled, but U.S. officials have left open the possibility the two men might talk on the sidelines of the international gathering.

If they do, it would mark the first meeting of U.S. and Iranian leaders in more than 30 years. A meeting could also be a precursor to renewed talks on Tehran's disputed nuclear program - though bridging differences over Iran's right to enrich uranium and maintain those stockpiles will be a far tougher task than arranging a handshake.

The election of Rouhani, a moderate cleric, signaled frustration among many Iranians with their country's international isolation and the crippling impact of Western sanctions. Obama and Rouhani have already exchanged letters. And the new Iranian president's rhetoric has so far been more palatable to the U.S. than former leader Mahmoud Ahmadinejad, who would threaten Israel as well as lambast the U.S. in his annual remarks at the U.N.

Trita Parsi, the president of the National Iranian American Council, said Rouhani shares with Obama a need to prove to a domestic audience that diplomacy can garner concrete results.

"If he can't show that his diplomatic approach will pay more dividends for Iran that Ahmadinejad's theatrics, then it's back to the conservatives being in the driver's seat. And the flexibility that Rouhani currently has will be lost," Parsi said.