Washington wants to rein in the spread of reprocessing and enrichment as it grapples with North Korea and Iran over their nuclear programs. It retains some suspicions about South Korea, which briefly pursued nuclear weapons in the 1970s and experimented with reprocessing later. Allowing South Korea to reprocess or enrich the fuel, the United States fears, would set a precedent for other nations and give North Korea a pretext not to abandon its nuclear weapons program.

“The Americans say no to recycling, but don’t offer an alternative,” said Lee Un-chul, a nuclear scientist at Seoul National University. “They think we might change our minds and build nuclear weapons, depending on the situation with North Korea. In short, they don’t trust us. This is frustrating. We have to fight.”

That tug of war begins later this year when the two allies start renegotiating their nuclear treaty, which expires in 2014. South Korea is the site of the next nuclear security summit meeting, in 2012.

Analysts here say that any new deal that would permit Washington to continue blocking South Korea from recycling its fuel  even though it has agreed to let India, which is not even a member of the Nuclear Nonproliferation Treaty, do so  would hurt the national pride of the South Koreans, who have been loyal allies.

According to local news reports, the South Korean government also wants to acquire a uranium enrichment capacity to make the traditional fuel for reactors  another activity banned by the 1974 accord because enriched uranium can also be used for weapons.