South Korea's top nuclear energy official on Tuesday denied claims that scientists in his country had produced near-bomb-grade uranium, seeking to ease concern that the previously undisclosed experiments were in apparent violation of international law.

"Yes, we did enrich uranium, but an amount so small it was almost invisible and to levels that were not close" to weapons grade, Chang In Soon, president of the government Korean Atomic Energy Research Institute, said in an interview. "This was an academic exercise, nothing more. We have no ambition beyond science. Any suggestion to the contrary is wrong."

His description of the experiments appeared to be at odds with testimony that South Korean officials are said to have provided last week to the International Atomic Energy Agency. Diplomats familiar with the testimony said the South Korean officials had reported that they enriched uranium to levels of almost 80 percent -- close to those used in nuclear weapons and far above the single-digit levels typically used in nuclear energy production.

Chang, however, insisted there had been a "misunderstanding." He said the three tests had yielded an average enrichment level of only 10 percent -- with the highest levels not exceeding the average by a large amount. Diplomats familiar with the case, however, said they preferred to await the results of IAEA testing.

Chang said he personally authorized the experiments -- a costly procedure that employs a laser to isolate certain uranium isotopes -- in January and February of 2000. The Seoul government reported the experiments to the IAEA last week.

The nuclear Non-Proliferation Treaty requires that signatories report any uranium-enrichment activities to the IAEA immediately. Not doing so is considered a serious violation. The IAEA, which is based in Vienna, dispatched a team to South Korea last week. Investigators collected half of the uranium that had been enriched -- about 100 milligrams -- and the IAEA said complete analysis was expected to take at least a month.

Several pounds of highly enriched uranium are required to build a bomb, according to experts. "If we had wanted to do it, we could have done it in another, more efficient way," Chang said. "But that wasn't our goal."

Even if South Korea is found to have enriched uranium to relatively low levels, the Seoul government may still face problems.

"On the surface, it appears to be a violation no matter what the enrichment level was," said a Vienna-based diplomat familiar with the matter. "But the consequences have a range, depending on what is found."

Officials at South Korea's Foreign Ministry said other high-ranking government officials were informed of the experiments in February by Chang, adding that the tests were not "government-sanctioned." But they deferred to Chang on the details of the experiments, which they reiterated had been quickly halted. Neither Chang nor the researchers involved had been disciplined, the officials said.

Chang said he chose to inform his superiors after reviewing an IAEA protocol adopted by the Seoul government this year that, according to his interpretation, had called for a higher level of accountability at South Korean nuclear facilities.

Chang said he authorized the tests after five South Korean scientists -- all of whom received their doctorates in the United States and who worked at the sprawling campus here 110 miles south of Seoul -- approached him for permission to enrich uranium. They were interested, he said, in "seeing what they could as scientists" with the institute's high-tech lasers and related equipment, all of which Chang said was about to scrapped. "As a scientist myself, I could not say no to them," he said.

"And I did not think this was a violation," he said. "This was such a small amount."

The case could complicate six-party negotiations over North Korean nuclear plans, as well as U.S. demands that the Iranian government disclose hidden portions of its nuclear programs.

The public and news media in South Korea, an important U.S. ally, have largely rallied around their scientists, with most newspapers condemning what was being portrayed here as an overreaction to the South Korean experiments. The country gets 40 percent of its power from nuclear energy but so far has refrained from enriching uranium itself, instead importing enriched uranium from the United States, Russia and elsewhere to feed its 19 nuclear power plants.