DAVOS, Switzerland - Iran plans to begin work next month on an underground uranium-enrichment facility as part of a plan to create a network of tens of thousands of machines turning out material that could be used to make nuclear arms, U.N. officials said yesterday.

The officials' comments were the first confirmation that work on the facility would begin in February. A senior U.S. State Department official warned that the move would be a "major miscalculation" by Iran.

"If Iran takes this step, it is going to confront universal international opposition," Undersecretary of State Nicholas Burns said. "If they think they can get away with 3,000 centrifuges without another Security Council resolution and additional international pressure, then they are very badly mistaken."

Former Iranian President Akbar Hashemi Rafsanjani, meanwhile, accused the United States of acting like a bully, with the aim of forcing Iran to abandon nuclear energy. In a sermon in Tehran, he said a U.S. military buildup in the Persian Gulf and the announcement that U.S. forces would seek to capture or kill Iranian agents in Iraq were aimed at Iranian nuclear programs.

"Today our enemies have come with several issues against us while having supporters in the world communities," Rafsanjani told worshipers. "This is bullying."

Also yesterday, the Iranian government said it would bar all U.N. inspectors from countries that voted in favor of a Security Council resolution last month that imposed sanctions on Iran for its nuclear program. Iran said it had rejected 38 names from a list of inspectors from the U.N. International Atomic Energy Agency.

Iranian officials have said repeatedly that work would start soon on the uranium-enrichment facility at the Natanz underground plant. There had been speculation the leadership might launch the project next month to celebrate the 28th anniversary of the Islamic Revolution, which brought the clerical leadership to power.

But the timing of the work may be a gesture of defiance. The Security Council's 60-day deadline for Iran to suspend uranium enrichment runs out next month, paving the way for further sanctions.

"I understand that they are going to announce that they are going to build up their 3,000-centrifuge facility . . . sometime next month," IAEA head Mohamed ElBaradei told reporters at the World Economic Forum.

U.N. officials, who demanded anonymity because the information was confidential, emphasized that Iran had not announced plans to begin assembling what will initially be 3,000 centrifuges at Natanz. But they said senior officials had informally told the IAEA that the work would begin next month.

Iran plans to expand its program to 54,000 centrifuges, which spin uranium gas into enriched material.

Iran says it aims to produce nuclear fuel to generate electricity. But if Iran chose, it could use the massive array of centrifuges to make enough weapons-grade material for dozens of nuclear warheads a year.

Diplomats briefed on the IAEA's findings said this month that the Iranians recently finished pre-assembly work at the Natanz facility, which is underground as protection against attack.

In enrichment plants, centrifuges are linked in "cascades." For now, the only known assembled centrifuge cascades in Iran are above ground at Natanz in two linked chains of 164 machines each and two smaller setups.

The two larger cascades have been running only sporadically to produce small quantities of non-weapons-grade enriched uranium, and the smaller assemblies have been underground "dry testing" since November, IAEA inspectors have reported.