The crisis over North Korea's nuclear weapons programs was initiated in 2002, when U.S. officials said North Korea had admitted violating a previous agreement by pursuing a nuclear weapons program based on enriched uranium. Now that six-nation talks may be producing progress in eliminating Pyongyang's far more advanced plutonium-based program, Washington has softened its tone about uranium enrichment. VOA's Kurt Achin reports from Seoul.

It was in October 2002 in Pyongyang that an eight-year-old U.S.-North Korea nuclear agreement known as the "Agreed Framework" screeched to a halt. U.S. officials presented North Korean negotiators with evidence that Pyongyang was violating the deal by undertaking a secret program to produce highly enriched uranium - HEU - presumably for use in nuclear weapons.

Tong Kim, then a high-level interpreter for the U.S. State Department, was in the room.

"What we said then was, we have convincing evidence. We said they were pursuing it. We didn't say how far they went, we didn't say they are producing HEU bombs," Kim said.

Kim, now an international relations professor here in Seoul, says North Korean officials acknowledged the program - something they have never done publicly, and which they now deny. He believes Pyongyang thought, erroneously, the acknowledgment would enhance their bargaining leverage with the United States.

Instead, it had the opposite effect. Washington halted fuel oil shipments to the North. Pyongyang ejected international nuclear inspectors in return, pulled out of the global nuclear Non-proliferation Treaty, and restarted the plutonium-producing reactor that had been shut down under the Agreed Framework.

China, Russia, the United States, South Korea and Japan subsequently initiated negotiations with North Korea - known as the six-party talks - to find a diplomatic end to the North's nuclear programs.

Since last month, when North Korea pledged to seal its main plutonium reactor once again, U.S. officials have indicated that Washington was reconsidering the HEU accusation that started the crisis.

The chief U.S. nuclear negotiator, Assistant Secretary of State Christopher Hill, told a Washington audience last month that the North will still have to answer for its purchase in the 1990's of uranium-related centrifuges from the network of Pakistani nuclear pioneer A.Q. Khan.

However, Hill implied that Washington might now be willing to accept that the centrifuges, and related aluminum tubes purchased from Germany, were not part of an HEU program at all.

"At some point we need to see what's happened to this equipment," Hill said. "If the tubes did not go into a highly enriched uranium program, maybe they went somewhere else - fine. We can have a discussion about where they are and where they've gone."

Hill says the United States simply isn't sure how far the North might have developed a uranium program.

"It's a complex program," he noted. "It would require a lot more equipment than we know that they have actually purchased. It requires some considerable production techniques, that, we're not sure they've mastered those."

Several weeks after Hill's comments, the main U.S. intelligence official dealing with North Korea, Joseph DeTrani, told the U.S. senate that Washington's confidence in the existence of a North Korean HEU program has decreased since 2002.

"The assessment was with high confidence that indeed, they [North Korea] were making acquisitions necessary for, if you will, a production-scale [uranium] program," he said. "And we still have confidence the program is in existence, at the mid-confidence level."

South Korea, too, believes the North has been working on an HEU program, but it, too, has no evidence that such a program is advanced. Last month, ending years of official silence on the issue, the South's chief nuclear negotiator, Chun Yung-woo, provided Seoul's first public assessment of the situation.

"We do not have full information where the program itself stands now." Chun said. "Nobody seems to believe that they have an enrichment plant up and running, but I cannot tell you how far North Korea's enrichment program has evolved."

Experts say there are several reasons for the apparent softening of the U.S. position.

First, U.S. intelligence suffered a major setback in Saddam Hussein's Iraq, where no weapons of mass destruction were found despite highly confident U.S. assurances. It is thought intelligence officials have decided to be more cautious in their conclusions.

Peter Beck, North Asia Director for the International Crisis Group, suspects North Korea's test of a plutonium-derived nuclear weapon last October also helped focus the minds of U.S. policymakers.

"After the nuclear test last October, they realized that the HEU program probably hasn't gone anywhere from when it was detected in 2002, and the plutonium program most certainly has," he said.

Experts like Beck say February's deal in Beijing is the outcome of a more pragmatic, plutonium-focused approach by Washington to the nuclear talks. The deal was signed only after intensive one-on-one discussions between the U.S. and North Korea in Berlin several months earlier.

Tong Kim, the former State Department interpreter, calls the HEU program accusations a "self-inflicted sticking point" by the United States. He says Washington is hoping to receive some form of explanation from North Korea, so the diplomatic process can move forward.

"What I would expect would be that North Koreans somehow would come up with an explanation of what they have bought and what they did with them - again, claiming that those materials, or their plan, had nothing to do with a weapons program," Kim said.

The International Crisis Group's Peter Beck says North Korea's uranium-related purchases are probably "sitting in a cave somewhere, gathering dust." He notes that the North must disclose details of all nuclear activities in the second phase of February's six-party agreement - although he predicts it will be reluctant to provide the kind of specificity the U.S. and its partners are looking for.

"Now, I'm not expecting the North to show up to a working group with a laundry list of their facilities, because that would essentially be handing over a target list to the Bush administration," Beck said. "So, how we get to that next step of coming clean is not going to be just a problem for HEU, but for all their other nuclear activities - and that's going to be a real challenge."

The deadline for implementation of the February agreement's first phase is mid-April. Talks on a second phase, which will include North Korea's promised nuclear declaration, are expected to begin shortly after that.