The United Nations General Assembly is due to decide whether to go ahead with drafting a treaty banning all forms of human cloning including research involving the cloning of human cells.
The campaign at the United Nations for a broad cloning ban has been led by the Bush administration and Costa Rica, with strong backing from the U.S. anti-abortion movement and many predominantly Catholic nations.
Opponents of a broad ban want a narrower approach prohibiting only the cloning of a human being, an idea that has almost universal support among the General Assembly's 191 member-nations.
But supporters of a broad global treaty rule out the option of a narrow approach, portraying so-called therapeutic cloning - in which cells from cloned human embryos are used in medical research - as the taking of human lives.
In a setback for the Bush White House, the assembly's legal committee decided by a one-vote margin last month to recommend that the writing of an international treaty banning cloning be put off for two years.
Backers of the delay argued there should be a broad global consensus on the treaty's goals before work begins.
The legal panel's recommendation now comes up in the full General Assembly, whose membership is identical to that of the legal committee. But Costa Rica said last week it would try to overturn the panel's vote.
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Supporters of a narrow human cloning ban predicted the Costa Rica group would fall short of the votes needed to prevail in the full General Assembly.
Some envoys said a compromise might yet emerge, to defer drafting of the treaty for one year rather than two.
The scientific community is lobbying UN missions to preserve the right to pursue therapeutic cloning, saying banning it would threaten a potentially promising field of research.