WASHINGTON — The State Department rejected Iran's latest proposal for international talks Thursday in another sign of trouble for the Obama administration's top-priority effort to engage Tehran in nuclear negotiations.
A five-page Iranian proposal distributed to foreign diplomats Wednesday "was not really responsive to our greatest concern, which is obviously Iran's nuclear program," said P.J. Crowley, the senior State Department spokesman.
At the same time, Crowley said, "We remain willing to engage Iran."
The administration faces an approaching deadline on whether to pursue a diplomatic opening with Iran, which was one of President Obama's trademark foreign policy ideas during his presidential campaign.
U.S. officials say Obama will decide by the end of the year whether to continue his offer of negotiations or withdraw it and step up sanctions to force the Islamic Republic to abandon its nuclear ambitions.
In the letter, Iranian leaders pledged to "embark on comprehensive, all-encompassing and constructive negotiations," but did not name the nuclear program as an issue for the talks. A copy of the letter was obtained by the nonprofit news organization ProPublica.
Tehran contends that it has the right under the Nuclear Nonproliferation Treaty to process uranium as part of a peaceful nuclear energy program, but U.S. and European officials allege Iran seeks to develop atomic weapons.
Though U.S. officials said there was still reason for hope, warning signs are mounting. Glyn Davies, the American ambassador to the U.N. nuclear monitoring agency, said Wednesday that Iran was now capable of quickly enriching its low-grade uranium to bomb-grade material if it wished.
Pressure is increasing on the Obama administration from conservatives and pro-Israel groups to take a harder line on Iran. Lawmakers are moving ahead with legislation to penalize companies that help Iran refine or import gasoline. Rep. Howard L. Berman (D-Valley Village), chairman of the House Foreign Affairs Committee, said after meeting with visiting Jewish leaders Thursday that he planned to move ahead with the bill.
The administration is quietly resisting the bill, arguing that it wants to hold off on tougher sanctions until it is sure that Iran cannot be persuaded to join in talks.
Meanwhile, a number of Iran specialists say the hard-line Iranian government's preoccupation with political rivals at home has made it less inclined to negotiate.
Ray Takeyh, who served as a senior State Department advisor on Iran until recently, noted that Iran's leaders have accused the West of meddling and stoking the protests over the disputed June presidential election that has divided the country.
"They're viewing the West through a very suspicious, if not conspiratorial, lens, which makes the possibility of compromise very difficult for them," said Takeyh, now with the Council on Foreign Relations.
George Perkovich, a nonproliferation specialist at the Carnegie Endowment for International Peace, said the significance of the week's developments is what it shows about Iranian intentions.
"What's becoming increasingly clear is that Iran is not interested in negotiations," he said.
Still, a senior U.S. official said that the political turbulence in Iran might also make President Mahmoud Ahmadinejad's government more open to a deal that would reduce international pressure.
"You can follow the logic of this two ways," said the official, who declined to be identified, citing the diplomatic sensitivity of the subject.
U.S. officials intend to confer with the five other world powers who have been trying to deal with the Iran issue -- France, Germany, Britain, Russia and China. Officials spoke Wednesday and are scheduled to meet again this month.
But there were new signs Thursday that the Russians, who have repeatedly balked at pressure to crack down on Iran, are unlikely to join a new sanctions effort.
Sergei Lavrov, the Russian foreign minister, spoke favorably of the Iranian letter, saying in Moscow that "my impression is that there is something there to use," according to Reuters.
Lavrov added that Russia would not take part in any international effort to halt refined oil deliveries to Iran, as some have proposed.
Alexander C. Hart of the Washington bureau contributed to this report.