WASHINGTON - The Obama administration and its European allies plan to open fresh negotiations with Iran by demanding the immediate closing and ultimate dismantling of a recently completed nuclear facility deep under a mountain, according to U.S. and European diplomats.

They are also calling for a halt in the production of uranium fuel that is considered just a few steps from bomb-grade, and the shipment of existing stockpiles of that fuel out of the country, the diplomats said.

That negotiating position will be the opening move in what President Obama has called Iran's "last chance" to resolve its nuclear confrontation with the United Nations and the West diplomatically. The hard-line approach would require Tehran's military leadership to give up the Fordo enrichment plant outside Qom, and with it a huge investment in the one facility that is most hardened against air attack.

Western 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.

Obama's aides are gambling that the negotiations, under the threat of Israeli military action, will finally force a resolution of the long-running debate inside Iran between those who want to pursue negotiated settlement -- and with it an end to crushing sanctions -- and those who believe engaging in the talks is tantamount to capitulation.

Haggling over the venue

The tensions among competing factions in Iran's leadership may explain the country's continuing haggling about the venue of the talks, planned next Friday. In recent days, Iran has changed its position and balked at holding them in Istanbul, demanding a move to what Tehran calls more neutral territory, like Iraq or China. U.S. and European officials say they have doubts about Tehran's readiness to negotiate seriously about stopping its nuclear-enrichment program and finally answering questions about its "possible military dimensions," including evidence that Iran may have worked on warhead designs and nuclear triggers.

The fear expressed in particular by Israel and some European leaders is that Iran will drag out talks to buy time while its centrifuges keep spinning deep inside mountain facilities, like the Fordo site. It is under so much granite that Israel fears it could create what Defense Minister Ehud Barak calls a "zone of immunity," where Iran could operate its nuclear program out of reach of Israeli bombs.

There is also disagreement among the Western allies about whether Iran's leaders have made a political decision to pursue a nuclear weapon. U.S. intelligence agencies have stuck to a 2007 assessment that found that Iran suspended research on nuclear weapons technology in 2003 and has not decided to take the final steps needed to build a bomb.

Same data, different take

But Britain and Israel in particular, looking at essentially the same evidence, say they believe a decision has been made to move to a nuclear weapons capability, if not a weapon itself.

While opening bids in negotiations are often designed to set a high bar, as a political matter U.S. and European officials say they cannot imagine agreeing to any outcome that leaves Iran with a stockpile of fuel that could be converted to bomb-grade in a matter of months.

The officials say that gives too little warning time if Iran made a political decision to build a weapon.

The outcome of the talks -- or their breakdown -- could well determine whether Washington will be able to quiet Israeli threats to take military action this year.

But talking with the mullahs also carries considerable political risk for Obama, as Iran is emerging as one of the few major foreign policy issues in the presidential campaign.