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(CNN) - Western diplomats and Iran appear to be inching toward a breakthrough deal that could slow the Middle Eastern nation's suspected progress toward a nuclear bomb while easing some sanctions that have hobbled its economy.
"Any deal is a big deal, given the last three decades-plus of tensions between the United States and Iran," said Richard Haass, president of the Council on Foreign Relations and former adviser to Secretary of State Colin Powell.
But, added Haass, any deal would likely be interim, and short-term, buying time "for a much more ambitious agreement that would be negotiated during that time span."
President Barack Obama has said easing sanctions against Iran is on the table.
"There is the possibility of a phased agreement in which the first phase would be us, you know, halting any advances on their nuclear program, rolling some potential back, and putting in place - a way where we can provide them some - very modest relief, but keeping the sanctions architecture in place, keeping the core sanctions in place," Obama said Thursday.
But Republican Sen. Bob Corker is trying to limit the administration's abilities to waive, or ease sanctions.
The administration is trying to thread the needle, says Haass.
"They've got to keep enough of the sanctions in place to keep the pressure on, any relief needs to be reversible. On the other hand, they've got to give the Iranians enough in order so they can defend the deal in their political system," said Haass.
The rewards that come with easing sanctions also cannot appear too big, relative to whatever Iran agrees to with this deal.
Treasury notices indicate that since Iranian President Hassan Rouhani was elected in June, the U.S. government has all but stopped the financial blacklisting of entities and people that help Iran evade international sanctions, according to reporting from The Daily Beast.
The move is likely a limited "confidence building measure," said Haass.
"In any negotiation, you often try to create an environment where you increase the odds, and that to me wouldn't be anything that's irrevocable," said Haass.
Israeli Prime Minister Netanyahu just met with Kerry, expressing his displeasure with the potential deal.
"Understand the Iranians are walking around very satisfied in Geneva, as well they should be, because they got everything, and paid nothing," said Netanyahu. "The international community got a bad deal, this is a really bad deal."
Netanyahu's public anger "is meant to toughen the U.S. position as you move toward the last hours, potentially, of negotiation," said Haass. The prime minister is also drumming up political support in Israel, said Haass, as well as in the U.S. – spurring congressman to scrutinize any sanctions relief for Iran.
And while "there's great nervousness," said Haass, the "devil's in the details," such as what assets will be frozen, how many centrifuges will Iran be allowed, whether the country can continue to produce uranium, or modernize any systems, and what kind of intrusive inspections will take place.
Once those details are addressed, then "we'll be able to say whether it's a fair deal, a balanced deal," said Haass.
"You've got to look at an interim agreement, and basically say do we get enough out of it, in terms of potentially what we put into it. And that's the only framework that everybody has to use," said Haass.
CNN's Jessica Metzger contributed to this report.