The director of the International Atomic Energy Agency (IAEA) urgently warned the United Nations yesterday that North Korea has recently accelerated its withdrawal of fuel rods from a nuclear reactor, raising new concerns about North Korean intentions.

During a series of negotiations with top IAEA officials this week, North Korea not only spurned the agency's demand that it halt the fuel rod withdrawal, but also said it could not accept demands for special storage of some key fuel rods, Hans Blix said in his letter to U.N. Secretary General Boutros-Boutros Ghali.

U.S. and IAEA officials have said that the fuel rods must be preserved for future radioactive measurements aimed at determining how much plutonium North Korea extracted in recent years from spent nuclear fuel. Plutonium is a key element in nuclear arms, and U.S. officials suspect North Korea of trying to develop an arsenal of such weapons.

The North Koreans told the IAEA that special storage of the withdrawn rods would not meet "their political constraints," Blix said.

Blix's letter, obtained by The Washington Post, warned that North Korea has withdrawn almost half of the reactor's estimated 8,000 fuel rods and is continuing to withdraw them "at a very fast pace ... not in line with the information previously conveyed to the agency." The agency had initially predicted the fuel withdrawal, which began two weeks ago, would not be completed for another six weeks.

Blix wrote that his agency's ability to inspect the rods would be "lost within days" if the North Koreans proceed as they have been. Unless North Korea changes its position immediately, he added, "the agency will not be in a position to verify the amount" of plutonium the country has accumulated or verify that North Korea is not developing a nuclear arsenal. He asked that the matter be brought immediately to the attention of the U.N. Security Council.

Robert Gallucci, the senior U.S. envoy for Korean matters, warned yesterday in an interview that if North Korea proceeded, Washington would cancel plans for new high-level talks desired by North Korea to chart a solution to the nuclear dispute and foster improved relations. Gallucci also said the continuing withdrawal of the fuel rods would "force us to go back to the Security Council where sanctions would be one of the options."

Other U.S. officials said they hoped China would intervene by sending a tough message to North Korea. In a sign of Washington's growing pessimism, however, U.S. officials yesterday began reviewing two draft statements condemning the North Korean action with other members of the U.N. Security Council.

The IAEA and U.S. warnings came after North Korean officials, at talks this week with mid-level U.S. diplomats in New York, rejected a U.S. proposal to begin the high-level talks promptly. The North Koreans complained that they could not accept Washington's condition that the talks could be held only if the key fuel rods were preserved.

North Korea's actions bolstered suspicions among some U.S. officials that the country is determined to hide how much plutonium it obtained by reprocessing spent fuel rods withdrawn from the reactor in 1989. Moreover, the officials said, if North Korea responds to sanctions by barring further inspections, it would then be able extract enough additional plutonium from spent fuel rods to manufacture four or five nuclear devices.

North Korean officials said their decision to reject the inspections was justified by the country's "unique status" under the nuclear Non-Proliferation Treaty, a global accord aimed at halting the spread of nuclear arms. North Korea claims it achieved this special status in 1993 by threatening to withdraw from the treaty and then suspending that threat under U.S. pressure.

The IAEA has repeatedly said North Korea has no special status and must comply with all the inspection pledges it made in January 1992. Among those pledges was a commitment to international verification of how much plutonium the country had extracted from spent fuel rods since the reactor started operating in 1986.

Two of the four IAEA negotiators in Pyongyang plan to depart for the agency's headquarters in Vienna today, with the other two staying behind at the site of the reactor in Yongbyon, north of the capital, to observe the withdrawal of fuel rods, Blix said.

If the fuel rods are pulled out, the agency would declare formally that it could no longer maintain adequate safeguards against nuclear weapons development there.

Secretary of State Warren Christopher told an Asia Society meeting in New York yesterday that "confrontation is emphatically not our preferred path." But he said if "North Korea rejects the negotiations we've offered," Washington would be well-positioned to "mobilize the international community to take sterner measures."

Christopher added that sanctions would "condemn" North Korea to continued isolation and economic deprivation, while preserving its status as a political pariah.