The hard-line approach would require the country’s military leadership to give up the Fordo enrichment plant outside the holy city of Qum, and with it a huge investment in the one facility that is most hardened against airstrikes.

While it is unclear whether the allies would accept anything less than closing and disassembling Fordo, government and outside experts say the terms may be especially difficult for Iran’s leaders to accept when they need to appear strong in the face of political infighting.

Still, Mr. Obama and his allies are gambling that crushing sanctions and the threat of Israeli military action will bolster the arguments of those Iranians who say a negotiated settlement is far preferable to isolation and more financial hardship. Other experts fear the tough conditions being set could instead swing the debate in favor of Iran’s hard-liners…

In interviews, administration officials said their “urgent priority” was to get Iran to give up — and ship out of the country — its stockpile of uranium enriched to 20 percent purity, and to get Tehran to close Fordo. Dismantlement, they said, would come in a second stage. So far Iran has produced only about 100 kilograms of 20 percent-enriched uranium — less than it would need to produce a single nuclear weapon — but it has announced plans to increase production sharply in coming months.