Strongly backed by the US anti-abortion movement and many predominantly Catholic nations, the campaign at the United Nations for a broad cloning ban has been led by the Bush administration and Costa Rica.
Opponents of a broad ban want a narrower approach prohibiting only the cloning of a human being, an idea that has virtually 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 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.
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.
Backers of the delay argued there should be a broad global consensus on the treaty's goals before work begins.
But the US maintains its supportive position of a total ban on human cloning, Richard Grenell, the spokesman for US Ambassador John Negroponte, told
Reuters news agency.
Negroponte stands for American
support of total ban on cloning
"If the Costa Rican proposal comes up, we will vote for it," Grenell said.
Supporters of a narrow human cloning ban, however, predicted the Costa Rica group would not gather the number of votes needed to prevail in the full General Assembly.
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.
While most scientists strongly oppose the cloning of a human being, "we must not allow those concerns to block medical advances that may some day be achieved through other kinds of research that involve cloned cells," said Alan Leshner, head of the Washington-based American Association for the Advancement of Science.
The broad approach backed by the United States and Costa Rica would ban "efforts to use cloned embryonic stem cells to try and generate healthy tissues, or to treat degenerative
diseases such as Parkinson's," he said.