The United States and Iran have agreed in principle for the first time to one-on-one negotiations over Iran's nuclear program, according to Obama administration officials, setting the stage for what could be a last-ditch diplomatic effort to avert a military strike on Iran.
Iranian officials have insisted that the talks wait until after the presidential election, a senior administration official said, telling their American counterparts that they want to know which American president they would be negotiating with.
News of the agreement — a result of intense, secret exchanges between American and Iranian officials that date almost to the beginning of President Obama's term — comes at a critical moment in the presidential contest, just two weeks before Election Day and a day before the final debate, which is to focus on national security and foreign policy.
It has the potential to help Mr. Obama make a case that he is nearing a diplomatic breakthrough in the decade-long effort by the world's major powers to curb Tehran's nuclear ambitions, but it could pose a risk if Iran is seen as using the prospect of the direct talks to buy time.
It is also far from clear that Mr. Obama's opponent, Mitt Romney, would go through with the negotiation should he win election. Mr. Romney has repeatedly criticized the president as showing weakness toward Iran and failing to stand firmly with Israel against the Iranian nuclear threat.
Reports of the agreement have circulated among a small group of diplomats involved with Iran.
There is still a chance the initiative could fall through, even if Mr. Obama is re-elected. Iran has a long history of using the promise of diplomacy to ease international pressure on it. In this case, American officials said they were uncertain whether Iran's opaque supreme leader, Ayatollah Ali Khamenei, had signed off. The American understandings have been reached with senior Iranian officials who report to him, an administration official said.
Even if the two sides sit down, American officials worry that Iran could prolong the negotiations to try to forestall military action and enable it to complete critical elements of its nuclear program, particularly at underground sites. Some American officials would like to limit the talks to Iran's nuclear program, one official said, while Iran has indicated that it wants to broaden the agenda to include Syria, Bahrain and other issues that have bedeviled relations between Washington and Tehran since the American hostage crisis in 1979.
"We've always seen the nuclear issue as independent," the administration official said, speaking on condition of anonymity because of the delicacy of the matter. "We're not going to allow them to draw a linkage."
The question of how best to deal with Iran has political ramifications for Mr. Romney as well. While he has accused Mr. Obama of weakness, he has given few specifics about what he would do differently.
Moreover, the prospect of one-on-one negotiations could put Mr. Romney in an awkward spot, since he has opposed allowing Iran to enrich uranium to any level — a concession that experts say is likely to figure in any deal on the nuclear program.
Beyond that, how Mr. Romney responds could signal how he would act if he becomes commander in chief. The danger of opposing such a diplomatic initiative is that it could make him look as if he is willing to risk another American war in the Middle East without exhausting alternatives.
"It would be unconscionable to go to war if we haven't had such discussions," said R. Nicholas Burns, who led negotiations with Tehran as under secretary of state in the George W. Bush administration.
Iran's nuclear program "is the most difficult national security issue facing the United States," he said, adding: "While we should preserve the use of force as a last resort, negotiating first with Iran makes sense. What are we going to do instead? Drive straight into a brick wall called war in 2013, and not try to talk to them?"
The administration, officials said, has begun an internal review among officials at the State Department, the White House and the Pentagon to determine the American negotiating stance, and what the United States would put in any offer. One option under consideration is "more for more" — more restrictions on Iran's enrichment activities in return for more easing of sanctions.
Israeli officials initially expressed an awareness of, and openness to, a diplomatic initiative. But when asked for a response on Saturday, Israel's ambassador to Washington, Michael B. Oren, said the administration had not informed Israel, and that the Israeli government feared Iran would use new talks to "advance their nuclear weapons program."
"We do not think Iran should be rewarded with direct talks," he said, "rather that sanctions and all other possible pressures on Iran must be increased."
Direct talks would also have implications for an existing series of negotiations involving a coalition of major powers, including the United States. These countries have imposed sanctions to pressure Iran over its nuclear program, which Tehran insists is for peaceful purposes but which Israel and many in the West believe is aimed at producing a weapon.
Dennis B. Ross, who oversaw Iran policy for the White House until early 2012, says one reason direct talks would make sense after the election is that the current major-power negotiations are bogged down in incremental efforts, which may not achieve a solution in time to prevent a military strike.
Mr. Ross said the United States could make Iran an "endgame proposal," under which Tehran would be allowed to maintain a civil nuclear power industry. Such a deal would resolve, in one stroke, issues like Iran's enrichment of uranium and the monitoring of its nuclear facilities.
Within the administration, there is debate over just how much uranium the United States would allow Iran to enrich inside the country. Among those involved in the deliberations, an official said, are Secretary of State Hillary Rodham Clinton, two of her deputies — William J. Burns and Wendy Sherman — and key White House officials, including the national security adviser, Thomas E. Donilon, and two of his lieutenants, Denis R. McDonough and Gary Samore.
Iran's capacity to enrich uranium bears on another key difference between Mr. Obama and Mr. Romney: whether to tolerate Iran's enrichment program short of producing a nuclear weapon, as long as inspectors can keep a close eye on it, versus prohibiting Iran from enriching uranium at all. Obama administration officials say they could imagine some circumstances under which low-level enrichment might be permitted; Mr. Romney has said that would be too risky.
But Mr. Romney's position has shifted back and forth. In September, he told ABC News that his "red line" on Iran was the same as Mr. Obama's — that Iran may not have a nuclear weapon. But his campaign later edited its Web site to include the line, "Mitt Romney believes that it is unacceptable for Iran to possess nuclear weapons capability." He repeated that in a speech at Virginia Military Institute this month.
For years, Iran has rejected one-on-one talks with the United States, reflecting what experts say are internal power struggles. A key tug of war is between President Mahmoud Ahmadinejad and Ali Larijani, Iran's former nuclear negotiator and now the chairman of the Parliament.
Iran, which views its nuclear program as a vital national interest, has also shied away from direct negotiations because the ruling mullahs did not want to appear as if they were sitting down with a country they have long demonized as the Great Satan.
But economic pressure may be forcing their hand. In June, when the major powers met in Moscow, American officials say that Iran was desperate to stave off a crippling European oil embargo. After that failed, these officials now say, Iranian officials delivered a message to their American counterparts that Tehran would be willing to sit down for one-on-one talks.
At the United Nations in September, Mr. Ahmadinejad hinted as much, describing the reasoning to American journalists. "Experience has shown that important and key decisions are not made in the U.S. leading up to the national elections," he said.
A senior American official said that the prospect of direct talks is why there has not been another meeting of the major-powers group on Iran.
In the meantime, pain from the sanctions has deepened. Iran's currency, the rial, plummeted 40 percent in early October.
Even with possible negotiations in the offing, there is no evidence Iran has slowed its fuel production. It continues to make nuclear fuel and has refused to allow international inspectors into key sites. Any negotiation with Iran, American officials say, would have to include highly intrusive inspection regimes.
—David E. Sanger contributed reporting.