North Korea and Pakistan are known to have exchanged weapons technology for years, so a transaction between them would not have been particularly shocking or new intelligence.

"Another Intelligence Fiasco," is how the English-language Korea Times referred to it in an article Wednesday. The conservative newspaper, Chosun Ilbo, has demanded an investigation.

"If the U.S. administration really offered false information … Washington's credibility and morality would be in tatters," the Chosun editorialized under the headline, "Did Washington Lie to Seoul?"

Although the South Korean government remained silent, the left-of-center ruling Uri Party issued a tough statement Tuesday accusing the Bush administration of destabilizing the Korean peninsula with its "distorted" intelligence and "oppressive" policies toward the North.

The State Department released a statement Tuesday in Seoul saying, "The United States has not misled allies or anyone else about the matter."

South Korean experts who have reviewed the U.S. evidence of a North Korean sale of uranium hexafluoride to Libya say it is a murky case.

For one, it is difficult to determine whether the uranium hexafluoride that was turned over by Libya as part of its nuclear dismantling originated in North Korea.

Even if it did, experts said, North Korea most likely had supplied the uranium hexafluoride to Pakistan and the rogue network of Abdul Qadeer Khan, that country's top nuclear scientist, had sold it to Libya.

"It looks like these were separate deals. North Korea supplied Pakistan. Pakistan supplied Libya. There is no evidence that North Korea knew anything about Libya," said a South Korean official who asked not to be quoted by name.

The official called the Washington Post story "70% correct."

He said the National Security Council's Asia director, Michael Green, who briefed South Korean officials, did disclose the Pakistani involvement, but at the same time he "aggrandized" North Korea's culpability.

The Libyans are believed to have acquired the uranium hexafluoride in 2001. North Korea has large reserves of natural uranium, but it is unclear whether it has the technology required to produce the gaseous uranium hexafluoride.

According to one expert, a large shipment of uranium hexafluoride was impounded two years ago in China on its way to North Korea, presumably for use in the North's own program to make highly enriched uranium. The incident implies that North Korea cannot produce its own.

In Vienna, scientists with the International Atomic Energy Agency have been testing the uranium hexafluoride turned over by Libya, but have not yet made a determination about its origin.

"Tests have not shown anything indicating that the uranium hexafluoride was from North Korea," a Western diplomat said.

Another Western diplomat said that a U.S. investigation was more thorough, and that through a process of elimination, the American scientists had ruled out other possible countries of origin for the gas.

North Korea announced Feb. 10 that it had developed nuclear weapons and that it would no longer participate in six-country talks over dismantling them.

Many South Koreans are jittery about the Bush administration's tough stance toward the leadership in Pyongyang, the North's capital. Along with the Chinese and Russians, they have been trying to nudge the U.S. into opening a one-on-one dialogue with Pyongyang and laying out more clearly what the benefits would be for the country if it were to dismantle its nuclear program.

Secretary of State Condoleezza Rice last week visited Tokyo, Seoul and Beijing, in large part to rally support for the U.S. line on North Korea, reassuring the region that there were no plans to attack the communist nation. But some of the gains from that trip might have been undone by the intelligence dispute.

"This is the last thing that the administration needs right now," said Daniel Pinkston, a nuclear expert with the Center for Nonproliferation Studies in Monterey, Calif. "It could really undermine U.S. credibility coming in the wake of all the questions about Iraq."

Times staff writer Douglas Frantz in Zurich, Switzerland, contributed to this report.