The compromise, which moves America closer to the positions of other nations selling nuclear technology and material, is important because it could give ammunition to Iran, which is under U.N. sanctions for defying a Security Council demand that it give up its enrichment program.
It also could complicate efforts to put life into a U.S.-Indian deal that would allow transfers of sensitive nuclear technology to New Delhi, even though it remains outside of the Nuclear Nonproliferation Treaty.
The diplomats, who demanded anonymity because their information was confidential, said the new U.S. position was discussed at a Vienna meeting of the 45-nation Nuclear Suppliers Group, whose gatherings are meant to set and monitor common policies on exports of sensitive atomic hardware and knowledge.
No decision was reached at the meeting, which ended Tuesday, said one of the diplomats, adding that any agreement must be made by consensus and that the issue was deferred to the group's next full session in Berlin starting May 19.
While the U.S. had moved closer to positions favored by most of the other NSG nations, the diplomat suggested there was still a ways to go if that consensus was to be achieved. Still, he said, Washington appeared to be prepared for further compromise.
"The U.S. will go back to Washington with some amendments, with some comments we put forward," he said. "The aim is to have a broad discussion in Berlin."
The U.S. decision to drop its insistence on a ban was forced primarily by Canada, which has large reserves of uranium and reserves the right to start up enrichment programs for lucrative export sales, the diplomats said.
Any ban, as originally demanded by the U.S., would thus present an obstacle to Canadian ambitions to possess its own enrichment capabilities.
The Americans, however, apparently remained firm in their opposition to any transfers of technology that is replicable and would allow receiving states to copy it and create their own program. A Canadian government statement issued while the meeting was still ongoing indicated that that was the case.
"While we welcome the U.S. proposal on nuclear enrichment and reprocessing, the proposal does not address all of Canada's concerns as a nuclear nonproliferation treaty party with impeccable nonproliferation credentials and a significant nuclear industry," said Foreign Affairs spokesman Andre Lemay. "We will continue to work with all parties in a nuclear supplies group to find an acceptable solution."
A participant in the meeting said the United States favored the "black box approach" that gives other nations the technologies without knowing how they work.
Canada wants the right to develop its own enrichment technology, and a ban on exports of replicable material — or the "black box approach" — would hurt it in this regard.
Other regional powers, such as Brazil, Argentina and South Africa, also have indicated a possible interest in selling enriched uranium fuel. With nuclear power undergoing a rebirth, additional countries might seek to join the club, a development that could lead to dozens developing enrichment programs and strengthen Iran's claim that it has the right as an NPT signatory to its own enrichment activities.
The U.S. shift also could hurt the chances that India can cut a deal with the suppliers group giving it greater access to nuclear technology even though it remains outside the NPT.
The U.S. wants the suppliers group to approve exports of nuclear fuel and technology to India, which has been cut off from international atomic markets because of its refusal to sign nonproliferation accords or accept outside inspection regimes.
An agreement meant to lead to that access for India was signed with the U.S. nearly two years ago. But it is in jeopardy, with India's leftist opposition arguing it would weaken the country's nuclear sovereignty.
Washington's shift could further complicate matters if it means moving closer to the position of other NSG states backing such sales but only on condition of more stringent international controls on recipients of such technology. That would surely strengthen Indian opposition to the deal, not only within the leftist opposition but also inside the government.
"The Indians have been insisting on having access through the NSG to enrichment and reprocessing-related technology and this propose, which is now being backed by the vast majority of NSG countries, would bar the transfer of these two technologies to India, which is not a member of the NPT," said Daryl Kimball executive director of the Arms Control Association in Washington.
Any tough safeguards on recipient countries would likely include acceptance of rigid International Atomic Energy Agency inspection rights — and in some cases at least, maintain a ban on sales of replicable technologies, said one of the diplomats.