By WILLIAM J. BROAD, DAVID E. SANGER and ELAINE SCIOLINO
VIENNA - International inspectors are requesting access to two secret Iranian military sites where intelligence suggests that Tehran's Ministry of Defense may be working on atomic weapons, despite the agreement that Iran reached this week to suspend its production of enriched uranium, according to diplomats here.
The inspectors at the International Atomic Energy Agency base their suspicions on a mix of satellite photographs indicating the testing of high explosives and procurement records showing the purchase of equipment that can be used for enriching uranium, the diplomats said. Both are critical steps in the development of nuclear arms.
The suspicions were aired here as an Iranian opposition group was preparing to release what it called new information that Iran was secretly developing a nuclear-capable missile whose range is significantly greater than what the Iranians have publicly acknowledged to date.
Iran has insisted that its uranium enrichment program is entirely for civilian nuclear energy production, but the areas the I.A.E.A. wants to visit are all in secure military bases. Traditionally, such facilities are considered off limits to the agency, whose primary mandate is to monitor civilian nuclear programs, unless there is strong evidence of covert nuclear activity at the military sites. Weapons experts cautioned that the equipment purchases and other activities could have nonnuclear purposes.
Mohamed ElBaradei, the director general of the I.A.E.A., said in an interview here on Wednesday that he had repeatedly asked Iran for access to the two sites, but that it had not yet been granted.
"We are following every credible piece of information," he said. Understanding the exact significance of what is happening at the two military sites is "important," he added. "We still have work to do, a lot of work." He estimated that even with full Iranian cooperation, it would take at least two years to resolve all of the outstanding questions surrounding the country's nuclear program.
"We're not rushing," he said. "It takes time."
The deal the Europeans signed with Iran, which the United Nations atomic agency blessed on Monday, was designed to defuse the most urgent problem, Tehran's enrichment of uranium at civilian sites, which could have given it quick access to the raw material for making bomb fuel.
With that problem at least temporarily under control, inspectors and the United States are now turning to the question of whether Iran has a parallel military nuclear program that it has not declared. Last year, the country admitted to inspectors that it had hidden critical aspects of its civilian program for 18 years.
The inspectors now want to examine the military sites to see whether secret nuclear work is under way. Much of the equipment needed for centrifuges - which spin at supersonic speeds to purify uranium for reactors and bombs - is "dual use," meaning it could be used for peaceful purposes as well.
Some officials close to the atomic agency said a last-minute disagreement over centrifuges in Iran's civilian program, which emerged before this week's accord was signed, may have been designed as a diversion by Tehran to take attention away from the agency's request for access to its military bases.
An Iranian official who was one of the negotiating delegation dismissed the idea of opening up the military sites, saying Tehran had no responsibility to do so. "There is nothing required for us to do," he said.
"They should have evidence that there are nuclear activities, not just 'We heard from someone that there is dual-use equipment that we want to see.' "
Diplomats and weapons experts here said in interviews that the intelligence on Iran's military activities came from several sources, including nations that are members of the United Nations nuclear agency.
One of the suspect military sites under investigation by the I.A.E.A. is a huge, decades-old facility southeast of Tehran, the Parchin military complex. Inspectors believe Iran's military may be testing conventional high explosives at the site, of a type used to detonate nuclear weapons.
If their suspicions are correct, inspectors say it could explain what Secretary of State Colin L. Powell was referring to nearly two weeks ago when he disclosed new American intelligence suggesting that Iran is working to shrink a nuclear device to a size that could fit atop the country's missiles.
While the United States has declined to discuss the intelligence Mr. Powell saw, the American representative to the I.A.E.A.'s board of governors, Jackie W. Sanders, at a meeting of the board on Monday, raised questions about Iranian efforts to obtain equipment "in the nuclear military area" and demanded a specific list of Iran's purchases "so we can make our own decisions about Iran's intentions."
But because there is no hard evidence now of actual nuclear material at Parchin, the international agency is left in the awkward position of asking Iran to admit its monitors to the site voluntarily, to prove what one European diplomat called "the absence of nuclear material."
The second site is a relatively new facility, called Lavisan II, built in northeastern Tehran, near the site of an older facility that was dismantled within the past year. The existence of the new facility was highlighted last month by an Iranian opposition group, the National Council of Resistance, the political front for the People's Mujahedeen. Even though the State Department has called the group a terror organization, American officials have been intrigued by the intelligence it has gathered on Iran's program.
Inspectors say they now possess procurement records showing that the military ordered a long shopping list of high-tech equipment for the Lavisan facilities - including specialized power supplies that smooth electrical currents to meet the exacting requirements of centrifuges.
A European diplomat who is dealing with the Iranian government on nuclear issues, said of the array of ordered equipment, "We believe it's related to enrichment and uranium conversion." He added that "it's something they need to explain for us."
The diplomat called the equipment orders "a little bit of everything" short of actual centrifuges. Each of the technologies on the order list, the expert said, had plausible uses both for nuclear and nonnuclear programs, making them "dual use" items.
"But when you combine them all together," he said, "it looks like a shopping list for an enrichment program."
He said it would make no sense for the military to buy the equipment on behalf of a civilian program. The more likely explanation, he said, was that the military itself "did the experiments," which would undercut Iran's argument that it has solely civilian nuclear projects under way.
The Parchin military complex has hundreds of bunkers, buildings and test sites scattered over a vast area about 20 miles southeast of Tehran. For decades, it has developed and made such things as ammunition, rockets and high explosives.
In September, the Institute for Science and International Security, an arms control group in Washington, issued a report claiming that Parchin contained "an isolated, separately secured site which may be involved in developing nuclear weapons."
The European expert on the Iranian program said that Parchin had helped develop Iran's long-range missiles and that evidence from satellite photographs and other sources suggested that some of its explosives work now centered on perfecting nuclear arms.
"If you go for nuclear weapons development, you need those places at a fairly early stage of your program," he said. International inspectors, he said, need to inspect the site rule out such work and "assure the absence of nuclear material."
Iran has so far refused to allow access to the military sites, even while denying that it has any hidden military program to develop nuclear arms.
European experts and diplomats said they remained hopeful that the Iranians might eventually permit access to the disputed military sites, citing past cooperation.
In October, 2003, they noted, Iran let the I.A.E.A. visit three locations at an industrial complex in Kolahdouz in western Tehran that the military controls. Despite rumors to the contrary, the inspectors found no work at those locations that could be directly linked to the enrichment of uranium. Moreover, the results of environmental sampling showed no signs of any use of nuclear materials.
One European official said the Iranians might be stalling for time to clean up the sites and remove all evidence of nuclear research.