U.S. Ambassador John Negroponte sent letters to ambassadors from about 100 countries that support a total ban, saying a delay would be "extremely unfortunate" and urging them to adopt the resolution when it comes up for a vote Thursday in the General Assembly's legal committee.
"There is a need to act now to confront the emerging threat of human cloning," Negroponte said, appealing to the ambassadors to vote against any motion to delay the resolution, which was sponsored by Costa Rica.
The cloning issue has deeply divided the 191-nation General Assembly, which traditionally seeks to reach a consensus on new treaties to generate the most support.
A rival resolution introduced by Belgium and co-sponsored by 23 countries including France, Germany, Britain, China and Japan, calls for a ban only on cloning to produce babies, leaving the question of human cloning for research and medical experiments to individual countries.
U.S. Deputy U.N. Ambassador James Cunningham said there was a fundamental difference of principle.
"Our view, and the view of the hundred or so supporters of the Costa Rican resolution is that it's a question of principle that the ban that we should be working on is total — and should cover both kinds of cloning," he said in an interview Friday.
The Costa Rican resolution would set up a working group to start drafting a treaty, and would establish the goal of a total ban on human cloning. It would not ban non-human cloning.
"What postponement really means is acquiescing in accepting that this research on cloning can continue without the majority of the General Assembly pronouncing itself in favor of a total ban, which will happen if we get a vote," Cunningham said.
The opposition to a total ban was initially led by France and Germany, who proposed a two-step approach. They argue that there is very strong international support for a worldwide ban on cloning babies, but less support for a ban on "therapeutic" cloning for research and medical purposes.
"Now there's a legal vacuum," said Belgian diplomat Marc Pecsteen, whose country is now leading the opposition. "Under our resolution, maybe there will be scientific cloning but at least it will be regulated."
But Pecsteen said that unless there is universal support for a treaty, it won't be effective, so "we think it's better not to have a vote on the issue because we are so divided."
Last week, the 57-nation Organization of the Islamic Conference decided to introduce a motion to postpone the cloning discussion for two years and Belgium will support it, Pecsteen said in an interview on Friday.
"If we wait, maybe it will become clearer whether scientific cloning has a future," Pecsteen said. "Some say it has tremendous potential, but it's opposed by other scientists."
Scientists supporting human cloning for medical purposes say they hope to use stem cells from human embryos to find cures for Alzheimer's, Parkinson's and other debilitating diseases. Stem cells, which are found in human embryos, umbilical cords and placentas, have not yet differentiated into any of the 220 cell types that make up the human body and so can divide and turn into any kind of cell in the body.
The Roman Catholic church and anti-abortion groups say stem cell research is tantamount to murder because it starts with the destruction of a human embryo.
Last year, President Bush restricted federal funding for human embryonic stem cell research to a select number of existing cells already harvested.
By Edith M. Lederer