Longer-Term Deal With Iran Faces Major Challenges LONDON - The Obama administration's successful push for an accord that would temporarily freeze much of Iran's nuclear program has cast a spotlight on the more formidable challenge it now confronts in trying to roll the program back. For all of the drama of late-night make-or-break talks in Geneva, the deal that Secretary of State John Kerry and his negotiating partners announced early on Sunday was largely a holding action, meant to keep the Iranian nuclear program in check for six months while negotiators pursue a far tougher and more lasting agreement. By itself, the interim pact does not foreclose either side's main options or require many irreversible actions - which was why the two sides were able to come to terms on it. That was also a reason for the sharp negative reaction the deal elicited on Sunday from Israel, an American ally that is deeply suspicious of Iranian intentions. Named the "Joint Plan of Action," the four-page agreement specifies in terse language the steps Iran would initially take to constrain its nuclear effort, and the financial relief it would get from the United States and its partners. A few technical details are left to footnotes. The agreement's preamble says that a more comprehensive solution is the eventual goal, and the broad elements of that solution are given in bullet points on the final page. The agreement allows Iran to preserve most of its nuclear infrastructure, and along with it the ability to develop a nuclear device, while the United States keeps in place the core oil and banking sanctions it has imposed. The questions that the United States and Iran need to grapple with in the next phase of their nuclear dialogue, if they want to overcome their long years of enmity, are more fundamental. Even the planned duration of the comprehensive follow-up agreement is still up in the air. It will not be open-ended, but there is as yet no meeting of the minds on how many years it would be in effect. The interim agreement says only that it would be "for a period to be agreed upon." "The terms of the comprehensive agreement have yet to be defined, but it is suggested that that agreement will itself have an expiration date," said Ray Takeyh, a former State Department official and a senior fellow at the Council on Foreign Relations. Iran's program to enrich uranium also needs to be dealt with in detail. The Obama administration has made clear that it is not prepared to concede at the start that Iran has a "right" to enrich uranium. But the interim deal, reflecting language proposed by the American delegation, says the follow-up agreement would provide for a "mutually defined enrichment program with practical limits and transparency." So the question appears to be not whether Iran will be allowed to continue enriching uranium, but rather what constraints the United States and its negotiating partners will insist on in return, and how large an enrichment program they are willing to tolerate. The interim accord makes clear that it must be consistent with "practical needs." Iran and the United States are likely to have very different ideas of what those needs are. "We will want very small and limited," Mr. Samore said, referring to Iran's enrichment efforts. They want industrial scale.