West and Iran Seen as Nearing a Nuclear Deal

After years of fruitless negotiations, Western and Iranian diplomats are on the verge of an agreement that would freeze Tehran’s nuclear program in exchange for an easing of some economic sanctions.

Secretary of State John Kerry is scheduled to travel here on Friday at the invitation of Catherine Ashton, the European Union’s foreign policy chief, in an effort “to help narrow differences,” a senior State Department official said. If that goes well, the pact could be announced later in the day, Iranian officials said.

But even as the two sides tried to finalize the agreement on Thursday, fissures have widened between the United States and some of its principal allies over the potential pact, which has been hailed by the Obama administration as a possible breakthrough in the standoff over Iran’s nuclear aspirations but dismissed by critics as a temporizing measure that would leave the core of Tehran’s atomic program intact.

Mr. Kerry and senior American officials here have promoted the idea of a multistage agreement as a hardheaded response to the new Iranian leadership of President Hassan Rouhani. The first phase of the accord would suspend Iran’s nuclear effort for as long as six months in return for limited sanctions relief, which could include access to frozen assets.

“We are asking them to step up and provide a complete freeze over where they are today,” Mr. Kerry said Thursday during a trip to the Middle East. “Iran knows that if they don’t meet the standards of the international community, the sanctions could be increased and even worse.”

Vigorously defending their approach, Obama administration officials cast the negotiations as a last, best chance to pull Iran back from the nuclear threshold, giving negotiators time to pursue a more sweeping accord.

Proponents say the deal has the potential not just to prevent Iran from building a nuclear weapon but also to open the way to a historic warming of relations between the nations, though American officials say there is no indication so far that Iran is willing to alienate traditional allies like the Shiite militant group Hezbollah or President Bashar al-Assad of Syria.

Critics, however, are not waiting for an agreement to be announced before denouncing it as a failure of will. On Thursday, Prime Minister Benjamin Netanyahu of Israel warned of a “grievous historic error” that he said would enable Iran to keep enriching uranium and preserve the option of developing nuclear arms while undermining support in the international community for economic sanctions.

“If the news that I am receiving of the impending proposal by the P5-plus-1 is true, this is the deal of the century, for Iran,” Mr. Netanyahu told a visiting delegation of American lawmakers, using the phrase for the world powers involved in the talks, and taking a stance that echoes similar worries in Saudi Arabia.

Mr. Netanyahu and other critics, in effect, fear that what the administration paints as a “first step” toward a more sweeping agreement may actually turn out to be the last. They have urged that the West retain and even toughen sanctions, until Iran is prepared to completely abandon its uranium enrichment ability and dismantle its nuclear program.

The outburst of controversy even before an agreement has been reached illustrates the tremendous difficulties the Obama administration faces in keeping a coalition together, especially one including Congress, throughout what promises to be a long and difficult diplomatic path to pursuing broader constraints on Iran’s nuclear operations.

Far from cooling passions over Iran, each step in the process seems to inflame them.

Robert Einhorn, a former State Department official who supports the administration’s negotiating strategy, dismissed as “not achievable” the maximalist approach advocated by Mr. Netanyahu.

“I don’t think any Iranian government could sell that deal at home,” Mr. Einhorn said during a conference call hosted by the Israel Project, a nonprofit organization that promotes Israel’s security. “I think we would pay a price in terms of the unraveling of sanctions if it looked like we, and not the Iranians, were the cause of the impasse.”

But Mark Dubowitz, the executive director of the Foundation for Defense of Democracies, said an interim agreement would go over badly with the allies and in Congress.

“Even if we get this de minimis interim deal from Iran, we could be in serious trouble,” he said. “The Israelis and Saudis are already freaking out about the dangers of any interim deal. This would demonstrate to them and Congress that the Obama administration has entered the Persian nuclear bazaar and gotten totally outnegotiated.”

Much of debate will turn on the technical details of the agreement, which is still being formalized. Iran’s foreign minister, Mohammad Javad Zarif, has repeatedly made clear that Tehran will not give up its “right” to enrich uranium, a point he reaffirmed in a CNN interview on Thursday night.

So the rigor of the initial understanding will turn on an array of thorny questions. How many and what type of centrifuges would Iran be able to retain to enrich uranium? Would Iran be barred from making additional centrifuges even if it did not immediately use them?

What would happen to the stockpile of uranium Iran has already enriched to 20 percent, which can be rapidly enriched to weapons grade? What sort of verification would be provided for?

Would Tehran be willing to suspend construction of a heavy-water plant that would produce plutonium? Such a step is important, experts say, because a military strike against the plant, should it come to that, could result in the dispersal of highly radioactive material if the plant was functioning.

David Albright, the president of the Institute for Science and International Security, provided a graphic illustration of what some measures could do to slow the advance of the Iranian program, but also how much of a risk might remain even if a “first step” accord is reached.

If an agreement did away with Iran’s inventory of uranium that was enriched to 20 percent, he said, it could add a month or somewhat longer to the time that Iran would need to produce enough weapons-grade uranium for a nuclear device, assuming Tehran opted to make a dash for a bomb.

The total “breakout time” to produce the needed weapons-grade uranium, he said, would be increased to about three months.

“I think it’s not a huge increase in the breakout timeline,” he told the conference call organized by the Israel Project. “But I think it is an important one to try to get.”