Officials hope to announce a final plan at a meeting of foreign ministers in Brussels on Monday.

But senior French officials are concerned that these measures, even in combination with sanctions on financial transactions with Iran announced by Washington, will not be strong enough to push the Iranian government into serious, substantive negotiations on its nuclear program, which the West says is aimed at producing weapons.

French officials say that the effort to increase pressure on Tehran is a crucial element in a “dual track” strategy — inflicting pain through sanctions in order to prompt substantive negotiations to halt Iran’s enrichment of uranium, as the United Nations Security Council has demanded. But even accelerated sanctions are hard to put into effect and slow to work, while Iran is changing the game by moving more of its enrichment centrifuges into deep tunnels inside mountains, where they will be much harder to attack militarily.

France is eager to avoid military action against Iran. French officials do not doubt that Israel will do all it can to prevent Iran from developing nuclear weapons, but they consider that an Israeli attack on Tehran would be counterproductive, only delaying the Iranian program and strengthening a weakened Islamic leadership.

“We must do everything possible to avoid an Israeli attack on Iran,” said a senior French official, “even if it means a rise in the price of oil and gasoline.” If the sanctions on Iran “are massive, they can have a big impact, with high unemployment and a fall in the rial,” Iran’s currency. In fact, the rial has hit historic lows against the dollar this week.

But with Iran moving its centrifuges deep underground, the official said, “this changes the landscape.”

“This time it really is a race. It’s why we are pushing so hard. We want to act fast.” Still, the official said, France recognizes that the possibility of military action represents another form of pressure on Iran to negotiate.

In his annual speech on French diplomacy on Friday, President Nicolas Sarkozy accused Iran of lying, and he denounced what he called its “senseless race for a nuclear bomb.” He called for “much stronger, much more decisive” sanctions, saying that “time is running out” and “everything must be done to avoid” international military intervention.

Iran says that it is enriching uranium solely for peaceful uses and denies a military intent. But few in the West believe Tehran, which has not cooperated fully with inspectors of the International Atomic Energy Agency and has been pursuing some technologies that have only a military use.

As existing sanctions bite, Tehran is talking both tough and soft, promising to shut the Strait of Hormuz in the case of an oil embargo and at the same time saying that it is ready to resume negotiations with the six-nation group, led by the European Union, which includes the five permanent members of the Security Council — the United States, France, Britain, Russia and China — plus Germany.

Russia and Turkey are already heralding Tehran’s willingness to return to the table. On Thursday, alongside the Iranian foreign minister in Istanbul, Turkey’s foreign minister, Ahmet Davutoglu, said that Iran was ready for talks. “The sides have confirmed their willingness,” he said. “Today is the day for negotiations and a solution.”

But French officials say that Tehran has not responded to an October letter from the European Union’s foreign policy chief, Catherine Ashton, offering a resumption of talks, so long as there are no preconditions and Iran is willing to discuss the main issue, which is its nuclear enrichment program.

During the last talks a year ago, Iran refused to discuss its nuclear program and said that before any negotiations, the Security Council must first lift all sanctions already in place and recognize Iran’s “right” to enrich uranium under the Nuclear Nonproliferation Treaty. Iran also said it was no longer interested in swapping a large part of its enriched uranium in return for fuel rods for a research medical reactor in Tehran.

Stephen Castle contributed reporting from Brussels, and Steven Lee Myers from Washington.

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