Under the American vision, Iran would halt all production of its 20 percent enriched uranium immediately, ship the existing stockpile out of the country and close the Fordow plant. That would defuse the threat of an Iranian “breakout” to produce a weapon, leaving the Iranians with a stockpile of low-enriched uranium that would require far more lengthy processing to weaponize.

Then the United States and its allies would offer some cooperation on civilian nuclear projects, and would agree not to add new sanctions at the United Nations Security Council. But the sanctions squeezing the Iranian economy would remain in place until a final deal is reached.

To the Iranians, this is a prescription for government change, and they insist it will fail. “I ask you sincerely, can anyone go to war with Iran,” even an economic war, and “come out a victor?” President Mahmoud Ahmadinejad said last week during a meeting with a half-dozen authors who have written books about Iran. “Why does the U.S. believe she can prevail?”

Yet Mr. Ahmadinejad declined to talk about the current negotiations. Instead, to the astonishment of Iranian officials, he argued at the session that the Iranian people were better off economically than they had been when he came to office. Since Mr. Ahmadinejad’s return to Tehran, Iranian officials have begun looking for any signs that their proposal, although rejected by Washington, could represent the basis of a conversation.

So far, it is difficult to find much overlap between the American and Iranian proposals. Both countries want to retain leverage, so the Iranians believe it is essential to keep the capability to produce uranium, and they reject any proposals to dismantle the nuclear infrastructure they have built, which they say is for civilian use. Similarly, the Americans, Europeans and Israelis believe they must maintain the constant pressure of sanctions.

On Wednesday, Secretary of State Hillary Rodham Clinton made it clear that the United States had no intention of relaxing the sanctions — particularly now, just as they show the first sign of forcing Iran’s leaders to rethink the costs of their nuclear program.

“We have always said that we had a dual-track approach to this, and one track was trying to put pressure on the Iranian government to come to the negotiating table,” Mrs. Clinton told reporters. But she said it was Iran’s own mismanagement of its economy, more than the sanctions, that deserved “responsibility for what is going on inside Iran.”

“And that is who should be held accountable,” Mrs. Clinton said. “And I think that they have made their own government decisions, having nothing to do with the sanctions that have had an impact on the economic conditions inside the country.”