"Iran's response indicates the balance has tipped in favor of more moderate voices in Iranian politics seeking a modus vivendi with U.S. power" in the region, said Kaveh Afrasiabi, an Iranian policy analyst who authored several books on the country's nuclear program.

That will not be easy, in part because the entire United Nations Security Council is supposed to vote on the sanctions package. While only the permanent members can veto, the rising fear, particularly among European diplomats, is that smaller countries on the Council are so angry over how the United States, and now France, have handled the Lebanon crisis that they will give Russia and China political cover to balk against imposing tough sanctions.

What is more, China and Russia both have energy companies invested in Iran, and they, along with European countries, would likely think hard before agreeing to prohibit the purchase of Iranian oil or to limit investment in Iran’s petroleum industry.

While there is no talk among the world powers right now about hitting Iran militarily, European diplomats in particular said they worried about a downward spiral if the sanctions did not work. “They’ve been dragged into three wars over there by the U.S.,” Mr. Parsi said, referring to Iraq, Afghanistan and Lebanon. “They don’t want a fourth.”