SEOUL, South Korea - North Korea announced yesterday that it would expel all international nuclear inspectors and restart a nuclear fuel reprocessing laboratory that outside experts fear could supply the isolated nation with weapons-grade plutonium.

Top officials in the Bush administration - which is pressuring the Russians, Chinese, Japanese and South Koreans to persuade North Korea to abandon its confrontational stance - conferred yesterday while the administration reiterated that Pyongyang must reverse course.

"The North Koreans would like nothing better than a dustup with the United States," said one senior Bush administration official. "That's the game they've played for years. We're not going to get into that."

Instead, Bush administration security advisers, emphasizing that the United States is not considering military action, decided to back an effort by the United Nations' International Atomic Energy Agency to lay North Korea's actions before the Security Council by declaring it in violation of international nonproliferation agreements.

In what is rapidly building into a test of international will against North Korean defiance, the atomic energy agency, which is headquartered in Vienna, Austria, said its three inspectors were "staying put."

It demanded that North Korea restore cameras and seals on four facilities that were shut down under a 1994 agreement designed to prevent North Korea from acquiring a nuclear bomb.

"Together with the loss of cameras and seals, the departure of inspectors would practically bring to an end our ability to monitor [the Democratic People's Republic of Korea's] nuclear program or assess its nature," said Mohamed ElBaradei, director general of the U.N. nuclear watchdog agency. "This is one further step away from defusing the crisis."

North Korea appeared increasingly isolated in diplomatic terms. South Korea's incoming president, who won election last week on a platform of greater engagement with North Korea, issued the strongest demand to date for the North to back down and play by international rules.

If the reprocessing laboratory is reopened, it will take North Korea about six months to start producing weapons-grade plutonium from 8,000 spent fuel rods that are stored in cans in pools of water, said Victor D. Cha, an expert on Korea at Georgetown University.

"If they kick out the inspectors the world has absolutely no eyes - no cameras, no inspections," said Cha, an associate professor of government. "The real red line is if they start doing something with that reprocessing plant. If they start tampering with those cans, everyone knows the timeline is six months."

But North Korea, through statements in its state-controlled news media and in a letter to the U.N. agency, showed every intention of kicking out the inspectors.

In the letter, Ri Je Son, director general of North Korea's Atomic Energy Department, cited as justifications for the move the suspension this month of an American-brokered deal to build two nuclear reactors in North Korea and the Bush administration's "designation of the DPRK as the 'axis of evil'" and the target for a "nuclear pre-emptive strike."

President Bush has publicly stated that the United States will not attack North Korea.

According to the International Atomic Energy Agency, one of the very few international bodies with any direct access to North Korea, technicians have moved a total of 2,000 new fuel rods into a building that houses a 5-megawatt experimental reactor.

North Korea has said that by the end of February it will restart the reactor, which produces plutonium as a byproduct. This week, North Korea also vowed to restart construction of two larger reactors, which are also of the plutonium-producing type.

In the letter, the North Korean nuclear chief said the reprocessing plant would be operated "as a preparatory step to secure safe storage of large quantity of spent-fuel rods that would come out once these power plants are in operation."

"It is for this sake that we will soon be prepared for the operation of the radiochemical laboratory," he wrote, referring to the processing plant.

Roh Moo Hyun, who takes office as president of South Korea in late February, said yesterday that the North's moves were undermining popular support for engagement with North Korea.

Meanwhile in Beijing, the English-language China Daily attacked a statement made earlier in the week by U.S. Secretary of Defense Donald H. Rumsfeld that the United States was capable of fighting two wars at once.

"This is a hawkish and dangerous warning," the newspaper said, taking a harsher line than the Chinese Foreign Ministry's appeal for dialogue. "It will poison the warming relations between the two sides on the Korean Peninsula."