Direct talks have the potential to ratchet down some of the pressure on President Obama over one of his greatest foreign policy challenges, the buildup of Iran’s nuclear program.

Mr. Obama has said that he will not permit Iran to have a nuclear weapon and has asserted that the use of military force is an option. Israeli officials have staked out a far tougher position, asserting that Iran should not be allowed to have the ability to build a weapon — and that the United States should do more to convince the Iranians that its threat to use force is credible. Israel has not ruled out military action of its own.

International sanctions have taken a serious toll on the Iranian economy and have helped bring Iran to the negotiating table, but have not yet extracted significant concessions from Iran on its nuclear program. For years, the United States and its partners — Britain, France, Germany, Russia and China — have met on and off with Iranian officials in a dialogue that has become known as the “P5 plus 1” talks.

Nonproliferation experts continue to argue that it is difficult to make major headway in such a committeelike forum, and that if progress is to be made, it will have to happen in private one-on-one discussions between Iranian officials and the Obama administration.

Whether Iran is genuinely interested in such talks, however, has been a subject of debate. In 2009, William J. Burns, then the under secretary of state for political affairs, met with Saeed Jalili, the Iranian nuclear negotiator, on the margins of the “P5 plus 1” talks. They agreed in principle that a portion of Iran’s enriched uranium could be used to make fuel for Tehran’s research center, which would preclude that material from being further enriched to make nuclear weapons.

But that deal fell through after Ayatollah Khamenei objected, and there have been no direct talks since. In a meeting this month with Iran’s departing president, Mahmoud Ahmadinejad, Ayatollah Khamenei was sharply critical of the American stance.

“The Americans are unreliable and illogical, and are not honest in their approach,” Ayatollah Khamenei said. But he also said that he did not oppose talks “on certain issues.”