WASHINGTON — With high-stakes negotiations over Iran’s nuclear program at an impasse, the Obama administration is under mounting pressure to rethink a diplomatic exercise that many argue is simply stringing along the rest of the world.

After two days of fruitless talks in Moscow, negotiators for the United States and other major powers did not even schedule another high-level meeting with Iran, committing only to a lower-level session in July to go over the technical details of a proposal to suspend the enrichment of uranium that Iran has already rejected in principle.

Dennis B. Ross, a former senior White House adviser on Iran, said he believed the negotiations had become a trap, allowing Iran to continue enriching nuclear fuel while the two sides fail to agree on even interim measures to slow the Iranian program. The major powers, he said, should scrap the step-by-step approach in favor of a comprehensive deal that would test Iran’s sincerity, but could also hasten a military confrontation.

“The issue here is, ‘How do you deal with a process that’s going to be harder and harder to justify?”’ said Ross, who left the administration in December and is now a senior fellow at the Washington Institute for Near Eastern Policy. “If it looks like you’re engaging in a process for the sake of process, that’s a bigger problem.”

Other critics are even blunter, labeling the talks a “charade” and demanding that Congress pass another round of sanctions against Iran. On Friday, 44 Republican and Democratic senators sent a letter to President Barack Obama urging him to abandon the negotiations if the Moscow meeting failed to produce any concessions from Iran.

“Talks are going slowly but Iran’s centrifuges are moving quickly,” said Rep. Brad Sherman, D-Calif. and member of the House Foreign Affairs Committee who has taken a tough line against Tehran.

Sherman said the U.S. should impose sanctions against all of Iran’s banks that go beyond unilateral measures aimed at cutting off its central bank. Those measures, which will take effect at the end of the month, could still cause a change of heart on the part of the Iranians, administration officials say.

These officials acknowledge that there are deep gaps between the two sides and no sign yet that the Iranians have made a genuine decision to bargain. But with the banking sanctions and a European Union oil embargo about to take effect, they insist that the step-by-step approach is worth pursuing a while longer.

At the working-level meeting, on July 3 in Istanbul, officials said they would seek further details on an Iranian proposal made in Moscow that left Western diplomats puzzled. The proposal was made in response to the demand that Iran suspend its enrichment of uranium to 20 percent, ship out its existing stockpile of that uranium and shut down its heavily fortified Fordo enrichment facility near the holy city of Qum.

While the Iranian offer made reference to 20 percent uranium, it was, in the words of a senior administration official, “elliptical.” And even though the diplomats met for hours on Monday and Tuesday, the official said there was not enough time to determine whether the Iranian offer held the prospect for progress.

“Iran submitted a good proposal to them,” Mohammad Reza Bahonar, a senior member of Iran’s Parliament, said at a news conference in Tehran.

Iranian officials and commanders reiterated that they would never relinquish what they called Iran’s nuclear rights. Some asserted that not only was Iran impervious to Western threats but was poised to prosper economically, despite evidence that the sanctions could cripple its ability to sell oil, its financial lifeline.

Such assertions do not mask the economic pain that analysts said was about to fall on Iran with the imposition of the oil sanctions. To some experts, that is reason enough to allow the diplomatic process to grind on.

“It looks hopeless now, but let’s not blind ourselves with our own rational Western culture,” said Cliff Kupchan, an Iran analyst at the Eurasia Group, a consulting firm. “This is a trading culture. It can turn on a dime.”

Ross, in an article published in The New Republic, argued that the major powers should skip all these steps and offer the Iranians a civil nuclear power capability that would be limited and monitored in a way that would not allow Iran to develop a weapon. If Iran rejected that offer, he said, it would clarify Tehran’s intentions.

Shifting to such an approach, Ross said, would also assuage the doubts of the Israelis, who say the Iranians are using the talks to buy time while they enrich fuel to use in bombs. And it would give the West sounder justification for a military strike on Iran’s nuclear facilities, since Tehran’s ultimate goal would no longer be ambiguous.

“For them to really feel they need to reach an agreement, they need to know that if diplomacy fails, the pressure is on them,” Ross said in a telephone interview from Israel, where he was meeting with Israeli officials.

Ross said he worried that the calendar, which initially worked against Iran because of the sanctions, was now in its favor. In particular, he said, the Iranians appeared to be calculating that Obama wanted to keep diplomacy going until after Election Day on Nov. 6. “They read the 6th as us not wanting diplomacy to fail,” he said.

Though Ross keeps lines to former colleagues at the White House, he has not persuaded the administration to change course. A senior administration official said pursuing a comprehensive deal would take months of negotiation, during which time Tehran would continue to enrich uranium. Agreeing on interim steps could freeze Iran’s enrichment sooner.

“Time is problematic,” said the official, who spoke on condition of anonymity because of the sensitivity of the talks. “As time moves on, it gets more problematic.”

© 2012 The New York Times Company