A Dec. 14 article misidentified the organization that first disclosed the existence of two Iranian nuclear facilities in August. It was the National Council of Resistance of Iran, an Iranian opposition group. (Published 12/15/02)

The White House expressed "serious concerns" yesterday about the construction of two nuclear facilities in Iran that officials say is part of a clandestine weapons program, adding to the growing list of nuclear headaches for the Bush administration.

The disclosure of the plants -- which appear designed to produce enriched uranium or plutonium, the fissile material needed for weapons -- came in the same week that North Korea announced it would restart a shuttered nuclear plant and the United States moved closer to confrontation with Iraq over its weapons programs.

White House spokesman Ari Fleischer said the Iranian facilities reinforce growing U.S. fears about Iran's "across-the-board pursuit of weapons of mass destruction and missile capabilities."

Despite the rising consternation about Iran's weapons programs, administration officials said yesterday they will keep their focus on the dispute with Iraq. They believe Iraq poses the greater threat, in part because of what they believe are stocks of chemical and biological weapons.

In an interview with CNN yesterday, however, the director general of the International Atomic Energy Agency, Mohamed El Baradei, said that in terms of the technical capability needed to produce nuclear weapons, he would rank North Korea and Iran ahead of Iraq.

U.S. officials said they will press for prompt inspections of the Iranian facilities and urge other nations to stop cooperating with Iran on nuclear matters. Officials were similarly restrained about North Korea's announcement, avoiding saber rattling as they embarked on a round of new diplomacy to isolate the regime.

Iranian officials yesterday denied the plants were part of a weapons program. They said the facilities had been fully disclosed to the International Atomic Energy Agency (IAEA) and were part of a plan to wean Iran's dependence on its oil reserves for energy.

U.S. officials rejected those assertions. "Our assessment, when we look at Iran, is that there is no economic gain for a country rich in oil and gas, like Iran, to build costly indigenous nuclear fuel cycle facilities," Fleischer said. "Iran flares off more gas every year than the equivalent power it hopes to produce with these reactors."

State Department spokesman Richard Boucher charged that Iran "tried to hide these important facilities" and has "repeatedly rebuffed IAEA requests for access to the sites." IAEA officials were to have visited the sites this week, but Iran suddenly delayed the inspections until February.

An Iraqi opposition group in August disclosed the possible existence of the two construction sites, and Newsday last month first reported rising U.S. concerns about the facilities and Iranian intentions. CNN on Thursday broadcast satellite photographs of the facilities, which were obtained by the Institute for Science and International Security, a research organization.

"These are certainly suspicious sites of concern," said one U.S. intelligence official.

U.S. intelligence officials knew about, and had been monitoring, the sites before they were revealed publicly, but they said it was impossible to know their precise stage of development until IAEA inspectors can get to the sites. Determining the extent of Iran's nuclear program has been, and remains, a priority for U.S. intelligence agencies.

In a report this week, the Institute for Science and International Security said the satellite photos suggested that one site, in Natanz, could be used to enrich uranium and that the other, in Arak, is a heavy-water plant, which would be part of a plutonium program.

"By their very nature, these types of facilities are dual-use," the report said. "They can be built as civil facilities and can be relatively quickly converted to produce material aimed at making nuclear weapons. Alternatively, they can be copied and built clandestinely."

In September, Iran informed the IAEA that it was pursuing a "long-term plan" to construct "nuclear power plants and the associated technologies such as fuel cycle" facilities. However, under its agreement with the IAEA, Iran is not required to allow IAEA inspections until six months before nuclear material is introduced in a facility. Iran has resisted signing an updated agreement that would require it to inform IAEA about any new facilities six months before construction is started.

Boucher said the satellite imagery indicated that portions of the Natanz plant -- including a service road, several small structures and three large structures -- were designed to be underground.

"Iran clearly intended to harden and bury that facility," he said. "That facility was probably never intended by Iran to be a declared component of a peaceful program; instead, Iran has been caught constructing a secret underground site, where it could produce fissile material."

Russia has been a big supplier to the Iranian nuclear program. U.S. officials have repeatedly pressed Russian officials to crack down on entities and individuals who have aided Iran's nuclear efforts.

Robert J. Einhorn, the top counterproliferation expert in the Clinton administration, said Iran's contention that it wants to develop a "closed fuel cycle" -- meaning not only reactors but also fabricating fuel and reprocessing fuel for reactors -- makes little sense, given the size of the Iranian program.

"The cost of purchasing fresh reactor fuel would be a tiny fraction of what it would cost to build fuel fabrication" facilities, given that Iran plans only a handful of reactors, he said.

Einhorn said the United States is aware that Iran has clandestinely tried to build its program. Iran has tried to buy a heavy-water reactor that could be used to produce weapons-grade plutonium from four countries, all of which turned it down, he said.

Einhorn said that Iran appeared to be hedging its bets, pursuing both plutonium and enriched uranium as routes to nuclear weapons. He said the big question is whether Iran has passed the point necessary to proceed with its programs without additional outside assistance.

Staff writers Dana Priest in Washington and Karl Vick in Istanbul contributed to this report.