Washington - The Obama administration announced an agreement on Tuesday with other major powers, including Russia and China, to impose a fourth set of sanctions on Iran over its nuclear program, setting the stage for an intense tug-of-war with Tehran as it attempts to avoid passage of the penalties by the full United Nations Security Council.

The announcement came just a day after Iranian leaders announced their own tentative deal, with Turkey and Brazil, to turn over about half of Iran's stockpile of nuclear fuel for a year, part of a frantic effort to blunt the American-led campaign for harsher sanctions.

"This announcement is as convincing an answer to the efforts undertaken in Tehran over the last few days as any we could provide," Secretary of State Hillary Rodham Clinton told the Senate Foreign Relations Committee, describing it as a "strong draft."

But even if the Security Council adopts these new sanctions, it is unclear whether the provisions - including a mandate to inspect Iranian ships suspected of entering international ports with nuclear-related technology or weapons - would inflict enough pain to force Iran to halt its uranium enrichment and cooperate with international inspectors. None of the past three sets of sanctions passed by the Security Council during the Bush administration succeeded.

Some of the toughest proposals were barely even discussed as the United States sought support from China, which is a major trading partner with Iran and has therefore been the most resistant to new sanctions. Along with Russia, the Chinese blocked any measure that would stop the flow of oil from Iranian ports, or gasoline into the country.

In the end, a deal was reached by the five permanent, veto-wielding members of the Security Council - the United States, Britain, France, Russia and China - plus Germany. They agreed on sanctions against Iranian financial institutions, including those that support the Islamic Revolutionary Guard Corps.

The American ambassador to the United Nations, Susan E. Rice, said, "We will seek a vote as soon as the conditions are right and council members have had an opportunity to consider it." Several officials said that moment would not come until next month, at the earliest.

Even if the sanctions survive without being watered down, administration officials concede they are unlikely to alter Iran's behavior, unless combined with considerable additional pressure. The previous three sets of sanctions were simply ignored by many of Iran's trading partners.

"The devil has been in the implementation," Patrick Clawson, the deputy director of research at the Washington Institute for Near East Studies.