WASHINGTON — President Barack Obama’s chief nuclear adviser said Friday that the United States and its allies planned new sanctions in an effort to test "Iran’s pain threshold" and force the country into suspending its production of nuclear fuel.

The adviser, Gary Samore, made his comments three days after talks with Iranian officials adjourned with no progress.

By increasing the economic pressure, White House officials say, they hope to raise the cost to the Iranian leadership of letting the talks drag on. But it is possible, some concede, that the Iranians could react by pulling out of the discussions. The talks, held this week in Geneva, were the first in a year, and are supposed to be followed by more meetings next month, probably in Turkey.

Samore suggested Iran may have decided to resume the talks with members of the U.N. Security Council and Germany "because it believes it can manipulate the appearance of negotiations to weaken existing sanctions and avoid additional measures."

"This ploy will not work," he said in a speech at a conference held Friday by the Foundation for the Defense of Democracies. "In the wake of the Geneva talks, we and our allies are determined to maintain and even increase pressure. We need to send the message to Iran that sanctions will only increase if Iran avoids serious negotiations and will not be lifted until our concerns are fully addressed."

Samore was not specific about the sanctions being considered.

Washington’s options are limited. Many European nations are reluctant to support the one step — limiting Iran’s oil exports — that many believe would hurt the regime the most because a true embargo would ripple through the world economy. The White House has been reluctant to impose curbs on the delivery of refined petroleum to Iran, fearing that gasoline shortages would make Iranian civilians more angry at the West than at their own government.

The current sanctions, imposed by the Security Council in the spring and embellished by the U.S., some European nations, Japan and Australia, are making it increasingly difficult for Iranian businesses and the government to conduct banking operations around the world, to get insurance for shipping lines and to refuel airliners at some airports in Europe.

But these sanctions have yet to persuade Iran’s leadership to heed the Security Council’s demands that the country stop enriching uranium and answer a series of questions from international nuclear inspectors.

Samore expressed optimism the situation could be changed. "I think what Iran is prepared to do will depend on their cost-benefit analysis," he said. "If the costs and the risks are high enough, they will accept suspension."

Some other Iran experts have disagreed, arguing that that the country’s senior leadership, and the Iranian Revolutionary Guard Corps, are less likely to give in under pressure.

Samore has been coordinating the effort to delay and ultimately derail Iran’s nuclear program. In recent weeks he has said that if Iran obtains a nuclear weapon, it could lead to proliferation in the Middle East and undermine Obama’s efforts to nudge the world to reduce nuclear stockpiles.

Asked about the effects of the Stuxnet computer worm, which appears to have been directed at disrupting Iran’s centrifuges, Samore was careful to avoid saying who might have been responsible for the attack.

But he added with a smile, "I’m glad to hear they are having troubles with their centrifuge machines, and the U.S. and its allies are doing everything we can to make it more complicated."

© 2010 The New York Times Company