TEHRAN, Iran - Iran said yesterday it was installing 3,000 centrifuges to enrich uranium at one of its nuclear facilities, effectively confirming that its nuclear program was running behind schedule as the devices were to have been in place two weeks ago.

Over the weekend, Iran dismissed reports from Europe that its uranium-enrichment program had been stalled. Enriched uranium is used as fuel in nuclear reactors and, at a higher degree of enrichment, can also be used to make atomic bombs.

But Iran had said the installation of the 3,000 centrifuges at its facility in Natanz, in central Iran, would be completed by the end of 2006. Its failure to do so has prompted reports that it is encountering technical difficulties in mastering large-scale enrichment.

Diplomats in Vienna, where the International Atomic Energy Agency is based, said Thursday that the enrichment program in Natanz had ground to a halt.

The diplomats said that suggested possible Iranian hesitancy to provoke U.N. Security Council sanctions harsher than the relatively mild penalties agreed on last month in response to Tehran's refusal to heed a council deadline to suspend enrichment.

Or, they said, it could be a sign of headway by relative moderates in the leadership unhappy with President Mahmoud Ahmadinejad's manner.

Some diplomats accredited or otherwise linked to the IAEA said some intelligence services believed the Natanz site could also be a front. While attention is focused on Natanz, Iranian scientists and military personnel could be working on a secret enrichment program at one or more unknown sites that is much more advanced, the diplomats said.

They spoke on condition of anonymity in exchange for discussing restricted information.

Other signs point to technical difficulties at Iran's nuclear facilities. Earlier this month, Vice President Gholamreza Aghazadeh, who heads the Atomic Energy Organization of Iran, told reporters that about 50 centrifuges had exploded during a test.

"We had installed 50 centrifuges," Aghazadeh was quoted as saying by Iranian media. "One night, I was informed that all the 50 centrifuges had exploded. . . . Ahmadinejad called me and said: 'Build these machines even if they explode 10 times more.' "

Gates: Iran Sees U.S. as Vulnerable

Defense Secretary Robert Gates said yesterday that new U.S. military moves

in the Persian Gulf were prompted in part by signals from Iran that it saw the United States as vulnerable in Iraq.

"The Iranians clearly believe that we are tied down in Iraq, that they have the initiative, that they are in a position to press us in many ways," Gates told reporters at NATO headquarters in Brussels, Belgium.

Gates indicated that Iran's view of U.S. vulnerability was part of the reason the Pentagon decided last week to send a second aircraft-carrier battle group and a Patriot antimissile battalion to the gulf. Patriots defend against shorter-range missiles of the type that

Iran could use to target

U.S. forces.

Laying out his concerns about Iran, Gates cited Iranian support for the radical Hezbollah movement in Lebanon. He also asserted that the Iranians "are doing nothing to be constructive

in Iraq at this point."

"My view," Gates said,

"is that when the Iranians

are prepared to play a constructive role in

dealing with some of these problems, then there might be opportunities

for engagement."

- Associated Press