A DEFIANT IRAN VOWS TO BUILD NUCLEAR PLANTS David E. Sanger reported from Washington, and William J. Broad from New York. Nazila Fathi contributed reporting from Toronto. WASHINGTON -- Iran angrily refused Sunday to comply with a demand by the U.N. nuclear agency to cease work on a once-secret nuclear fuel enrichment plant, and escalated the confrontation by declaring it would construct 10 more such plants. The response to the demand came as Iran's president, Mahmoud Ahmadinejad, said his Cabinet would also order a study of what it would take for Iran to further enrich its existing stockpile of nuclear fuel for use in a medical reactor -- rather than rely on Russia or another nation, as agreed to in an earlier tentative deal. While it is unclear whether Iran has the fuel technology, the declaration appeared intended to convince the West that Iran was prepared to move closer to bomb-grade quality, while stopping short of crossing that threshold. Even if Iran proceeded with an ambitious plan to build 10 enrichment plants, it is doubtful Iran could execute that plan for years, maybe decades. But the announcement itself was enough to draw immediate condemnation from the White House, which clearly hoped that Iran's defiant tone would help convince Russia and China that imposing harsh sanctions was justified. Both countries, historically opposed to sanctions, had voted in favor of a resolution by the International Atomic Energy Agency, the U.N. nuclear monitor, demanding that Iran stop work on a formerly secret enrichment plant. By refusing to accept that resolution, one senior administration official said, 'Ahmadinejad may be doing more to assemble a sanctions coalition than we could do in months of work.' The White House spokesman, Robert Gibbs, said of Iran's declaration: 'If true, this would be yet another serious violation of Iran's clear obligations under multiple U.N. Security Council resolutions, and another example of Iran choosing to isolate itself.' According to Iranian state television, Ahmadinejad's Cabinet voted to begin construction at five new sites designated for uranium enrichment plants -- it did not specify where -- and to determine locations for another five in the next few months. In Europe, diplomats called the Iranian plan for a giant expansion of enrichment closer to a national aspiration than an imminent threat. Iran's main enrichment facility, at Natanz, began early this decade and today the country has installed fewer than a tenth of the 50,000 centrifuges it is designed to handle. A second, once-secret plant -- revealed two months ago -- has been under construction for more than three years, and it is still at least a year from completion. 'It's preposterous,' a diplomat in Vienna who collaborates with the International Atomic Energy Agency said of the plan for the 10 plants. The diplomat, who closely monitors the Iranian nuclear program, added: 'It would be way, way more than they need no matter what their nuclear aspirations.' He noted that the United States had just one enrichment plant, in Paducah, Ky. But the threat did appear to represent Iran's decision to find a way to strike back politically at the West for the Security Council's three resolutions demanding that Iran stop all enrichment activity. The international atomic agency's board built on those Security Council resolutions on Friday, when it demanded that Iran halt work on construction of its second, once-secret enrichment plant. It was the first time the atomic agency had told Iran to halt construction of a plant. What American and atomic agency officials fear is that the steady drumbeat of defiant declarations from Iran could lead to the one act that would truly touch off a crisis: Iran's withdrawal from the Nuclear Non-proliferation Treaty. That would terminate the already limited presence of the West's atomic inspectors in Iran. North Korea took that step in early 2003, and soon produced the fuel for eight or more nuclear weapons; it has since tested two. More than 200 members of the Iranian parliament signed a letter on Sunday, according to Iranian press accounts, urging that the atomic agency's presence in Iran be further restricted, and individual political leaders have called for withdrawal from the nonproliferation treaty. But Iran may be hesitant to follow North Korea's lead. Such a declaration would signal to the world that Iran was heading for 'nuclear breakout,' a rush to produce a bomb. Such a declaration would almost certainly build pressure for sanctions, and could lead to pre-emptive military action against Iran by Israel. 'You have to think,' one of President Barack Obama's top national security advisers said recently, 'that they would think twice before denouncing their treaty obligations.' Instead, the speaker of Iran's parliament, Ali Larijani, who once led Iran's nuclear negotiating team, warned Sunday that Iran's cooperation with the agency could 'seriously decrease' in the near future. Tehran says its nuclear program is peaceful, and to date has enriched uranium to a relatively low grade consistent with making fuel for a civilian nuclear power plant. But so far, there are no civilian nuclear plants under construction to receive that fuel; the two plants Iran is getting ready to open, at Bushehr, receive fuel from Russia. The absence of civilian reactors is one reason Western analysts suspect that Iran's real intentions are to make atom bombs. Iran has long talked of building as many as 19 more nuclear plants in addition to the complex at Bushehr. In the past, the plan for a total of 20 power plants resulted in a large gap between Iran's declared ambitions and its envisioned needs for enrichment, and Sunday's announcement sought to end that contradiction, at least in theory. Western nuclear experts said that taking the declaration of the 10-plant goal at face value was akin to believing in the tooth fairy. 'They're hyping it,' said David Albright, president of the Institute for Science and International Security, a private group in Washington that tracks nuclear proliferation. 'They couldn't build that number of centrifuges. They don't have the infrastructure.' Albright added that Iran's supplies of uranium were dwindling, casting more doubt on the vastly expanded commercial fuel goal. The result, he said, is that the new push for enrichment will probably end up producing 'one small plant somewhere that they're not going to tell us about' and be military in nature. 