Iran Nuclear Negotiators, Facing Deadline and Differences, Weigh Extending Talks VIENNA - With a deadline for an agreement to curb Iran's nuclear program just a day away, Western and Iranian officials on Sunday finally acknowledged that they might be too far apart on the most contentious disputes and began to wrestle with the politically charged issue of how to find terms for extending the talks a second time. A member of Iran's negotiating team told the Iranian news media that if an understanding on the broad elements of a comprehensive agreement was not within reach by Sunday evening, the option of extending the agreement "will be on the table." A Western diplomat said that the question of prolonging the talks had not yet been raised with the Iranian side, but that a number of options were already being discussed by American and European officials. And the Western diplomat, who spoke on the condition of anonymity to talk about the internal deliberations, said it was expected that the question would be taken up with Iranian officials by the end of the day. On Sunday, President Obama said that the gaps in the negotiations were still "significant." Mr. Obama appeared to rule out giving in to one of Iran's key demands: that as part of any final deal, the United States and its partners lift, quickly and permanently, all the nuclear-related sanctions against Tehran. "I think Iran would love to see the sanctions end immediately, and then to still have some avenues that might not be completely closed, and we can't do that," said Mr. Obama, referring to avenues for producing a nuclear weapon. But he also held out hope that an agreement, if it could be struck, would change the nature of the relationship with Iran for the first time in more than three decades. "What a deal would do," he said, "is take a big piece of business off the table and perhaps begin a long process in which the relationship not just between Iran and us but the relationship between Iran and the world, and the region, begins to change," Mr. Obama said in an interview broadcast Sunday on ABC. "These are the hours of truth," the German foreign minister, Frank-Walter Steinmeier, said on Saturday. We have to check now if Iran is really ready to move in the right direction. The decision of when and under what conditions to agree to a negotiating extension has been a highly delicate one for the Obama administration, which would like to lock in many areas of agreement that negotiators for the two sides have spent months drafting and are now waiting for political decisions from Iran's supreme leader, Ayatollah Ali Khamenei, and Mr. Obama. But given the failure to close the wide gap that still remains, experts have said for days that an extension was all but inevitable. The Iranians have reportedly declined to agree to dismantle a significant number of their centrifuges - the machines that enrich uranium at supersonic speed - and the United States and its negotiating partners have refused to promise a rapid, permanent end to economic sanctions against Iran. Mr. Obama has said he would suspend American sanctions step by step, as Iran complies with its obligations. The key issues in the talks also include how many years an agreement would last before Iran would be free, like any other signer of the Nuclear Nonproliferation Treaty, to develop as large a civilian nuclear infrastructure as it would like. For weeks, the American team has sought to keep the pressure on the Iranians to make hard decisions in the talks by insisting that an extension was not on the table, though the possibility has always lurked in the background. "We are not talking about an extension," Secretary of StateJohn Kerry insisted as recently as Thursday. Republican and even some Democratic lawmakers have warned that they would press for additional sanctions if the American negotiating team did not emerge from the latest round of talks with provisions that toughened the temporary agreement. That agreement freezes much of Iran's nuclear program and is set to expire on Monday. The Obama administration already agreed to one extension, in July, which it justified on the grounds that sufficient progress had been made to warrant continuing the talks until Nov. 24, the anniversary of an agreement for a temporary accord that froze some of Iran's advances and required Iran to dilute a stockpile of fuel that the West feared could quickly be converted to weapons use. That extension was explicitly permitted under the terms of the temporary accord. But there is no provision for an extension beyond a year, and the administration is struggling to identify additional progress that would justify another one. Photo Iranian negotiators have expressed concern about President Obama's ability to deliver an agreement that will survive contact with a skeptical Congress. Credit Stephen Crowley/The New York Times A breakdown in talks, American and Iranian officials seem to agree, is in neither side's interest. Any extension that might be agreed to would presumably keep in place the freeze on much of Iran's nuclear program and could be cited by the White House to make the case to Congress against additional sanctions. It would also enable the United States to argue to Prime Minister Benjamin Netanyahu of Israel - whom Mr. Kerry called on Saturday - that there is no need for military action because Iran's nuclear threat is less than it was a year ago. But the temporary accord was never envisioned to be permanent. And in Tehran, where the issue is whether negotiators can win an end to the economic sanctions, an extension would probably not allow Iran to sell more oil on international markets or resume normal banking relationships with the West. The key question is what form an extension might take. With American officials saying that their goal in the talks is to lengthen the "breakout" time Iran needs to produce enough fissile material for a nuclear weapon to at least a year, the best option for American officials would be to conclude a broad understanding on the main elements of a comprehensive accord and to thrash out the details over the next few months. The option that would be the most difficult to sell would be a straight extension without any clear headway on the remaining stumbling blocks. In between are an array of possibilities, which may only emerge as the negotiators work into the night. On Wednesday, Philip Hammond, Britain's foreign secretary, suggested that the goal might be an agreement that could codify "significant movement" during the current round of talks while putting more time on the clock to pursue a comprehensive accord. While American officials were unwilling to say publicly last week that they would be satisfied with such an outcome, as of Sunday it appeared to be the most that might be achieved. On Sunday morning, Mr. Kerry met here with Mohammad Javad Zarif, Iran's foreign minister, and Catherine Ashton, the European Union's envoy to the talks. It was the fifth such meeting in recent days for Mr. Kerry, who planned to attend a working dinner Sunday night with Ms. Ashton, Mr. Steinmeier and his British and French counterparts, who are rejoining the talks here. Mr. Kerry also drove to the airport here Sunday to talk with Saudi al-Faisal, the Saudi foreign minister. The Saudi diplomat, who had met with Mr. Kerry in Paris on Thursday, flew here for another update on the talks and the two diplomats talked on his plane, which was parked on the Vienna airport tarmac. While Saudi Arabia is not involved in the talks, it has long been worried that an agreement might allow Iran to keep more of its nuclear infrastructure that Saudi Arabia is comfortable with. Russia's foreign minister, Sergey V. Lavrov, flew here Sunday to join the talks. An Iranian negotiator, who was not named, was quoted by an Iranian news agency on Sunday as saying that a detailed and comprehensive agreement was no longer possible by the Monday deadline. The Iranian held out the hope that a general understanding on the main elements of an agreement, such as the number of centrifuges and a plan for ending sanctions, might yet be possible, though there was nothing in his comments to indicate that Tehran was yet prepared to make the sort of concessions that the United States says are needed. "If by Sunday night here in Vienna we don't agree on a general and political understanding," the Iranian official told the Iranians Students" News Agency, the option of extending the talks "will be on the table." The Iranian official did not say how long such an extension would last, but an Iranian negotiator was quoted by Agence France-Presse as saying that it might be for six to 12 months. "We must absolutely avoid a climate of confrontation with escalation from one side and the other," the Iranian official, who was not named, told the French news agency.