The Bush administration won't back down on pursuing new sanctions against Iran over its nuclear program despite questions about their usefulness raised by government auditors, U.S. officials said.

Secretary of State Condoleezza Rice will press Washington's case for fresh U.N. sanctions next week in Europe even as the U.S. considers imposing more penalties of its own to step up pressure on Tehran to halt activities that could lead to the development of a nuclear weapon.

Announcing Rice's Jan. 22 meeting in Berlin with her foreign minister colleagues from the four other permanent members of the U.N. Security Council and Germany, the State Department said Wednesday the United States had no plans to change its sanctions strategy in dealing with Iran even after Congress' investigative arm said the impact of the policy was unclear.

"The whole strategy here is to use various kinds of diplomatic pressure at a gradually increasing rate to try to get a different set of decisions out of the Iranian leadership," spokesman Sean McCormack told reporters.

The administration has unsuccessfully lobbied for the Security Council to pass a third Iran sanctions resolution for nearly a year but has faced stiff resistance from Russia and China, which have been unwilling to agree to either the language or timing of such a move. Chinese and Russian opposition to sanctions has been hardened by the findings of a U.S. National Intelligence Estimate that said Iran stopped working on a secret nuclear weapons program in 2003.

Deputy Secretary of State John Negroponte, who was to raise the issue of new sanctions Thursday in Beijing with Chinese Deputy Foreign Minister Dai Bingguo, said the intelligence estimate showed only that Iran has suspended work on warhead design but was pressing ahead on uranium enrichment and missile development.

"Work continues by Iran on two out of those three parts of that program," Negroponte told reporters in Beijing before departing for the talks. "So we think it's important that there be an additional Security Council resolution because Iran is out of compliance on previously passed resolutions," he said.

McCormack refused to speculate as to whether Tuesday's gathering of the foreign ministers of Britain, China, France, Germany, Russia and the U.S. would produce a new resolution.

The meeting will be the first of its kind in four months, since the ministers last met in late September in New York on the sidelines of the U.N. General Assembly, and will be the first since the release of a U.S. intelligence report in December that determined Iran had actually stopped efforts to develop nuclear weapons in 2003.

President George W. Bush and his top aides have said repeatedly that they still believe Iran is a threat and that it must agree to international demands to halt uranium enrichment and reprocessing, which could give the country the means to produce atomic weapons.

The push to contain Iran has been given new urgency by an incident in the Persian Gulf this month in which U.S. warships were harassed by the Iranian naval speedboats in the Strait of Hormuz.

Senior Pentagon officials briefed House members and Senate staff on Wednesday about that confrontation. Attendees were prohibited from discussing details from meeting, which was classified, but said much of what was presented had already been released by the Defense Department.

Rep. Robin Hayes, a Republican, said the big question left unanswered is whether Tehran orchestrated the confrontation.

"It becomes speculation about how much planning, how much forethought was there, and who was in charge," he said.

A senior Iranian official said Tehran is confident of a prompt solution to the dispute but warned that failure would play into the hands of those who favor unilateral action and war and criticized Bush for speaking "constantly about war."

Ali Bagheri, Iran's deputy foreign minister, noted that the last report from Mohamed ElBaradei, chief of the International Atomic Energy Agency, showed that some of the issues surrounding Tehran's nuclear program had been resolved. He also pointed to the findings of the U.S. intelligence report.

The Government Accountability Office released a report Wednesday that questioned the impact of unilateral U.S. sanctions — including a wide array imposed on banks, parts of its military and senior officials — on Iranian behavior.

"U.S. officials report that U.S. sanctions have slowed foreign investment in Iran's petroleum sector, denied parties involved in Iran's proliferation and terrorism activities access to the U.S. financial system, and provided a clear statement of U.S. concerns to the rest of the world," the report said.

"However, other evidence raises questions about the extent of reported impacts," the GAO said.

It noted that since 2003, the Iranian government has signed contracts reportedly worth about $20 billion with foreign energy firms and that sanctioned Iranian banks are funding their activities in currencies other than the dollar.

At the same time, it said that Iran continues to enrich uranium, acquire advanced weapons technology, and support terrorism. And, the report added that U.S. agencies do not systematically collect or analyze data demonstrating the overall impact of the sanctions.

McCormack maintained that sanctions are effective even if they take time to produce results.