A tiny majority dealt the setback to the Bush administration on Thursda. By a margin of 80 to 79 with 15 absentions, the General Assembly’s legal committee voted to defer the treaty until 2005.
Iran proposed the delay on behalf of the 57-nation Organisation of Islamic Conference.
The matter has been pending in the 191-nation assembly since 2001, when France and Germany asked the United Nations to quickly draft a treaty banning human cloning - a goal with virtually unanimous support in the international community.
But Washington, with backing from the US anti-abortion movement, then shattered that consensus by ruling out any treaty unless it banned both cloning humans and "therapeutic"
cloning, in which human cells are cloned for medical research.
Cloning research relies on embryo cells, or stem cells, because they can grow into all cells and tissues in the body.
Washington, with help from Costa Rica, eventually claimed the support of as many as 100 nations for a resolution instructing treaty drafters to prepare a total ban on cloning.
A UN committee blocked the US-
A smaller group - led by Belgium and including Brazil, Japan, South Africa and other European states - then emerged to push for a narrower ban exempting therapeutic cloning.
The latter group - which includes Britain, the United States' closest ally on most other international issues - argued the top UN priority should be to quickly ban cloning
humans, leaving it to individual governments to decide whether - and if so, how - to regulate therapeutic cloning.
Washington's foes also noted that the US Congress was itself so deeply divided over stem cell research that it had so far failed to adopt legislation regulating it.
Thursday's UN vote showed the depth of the split, particularly in Europe, where Austria, Ireland, Italy, Portugal and Spain backed Washington while Belgium, Britain, Denmark, Finland, France, Germany, Greece, Luxembourg, Netherlands and Sweden voted for a delay.
Canada, which backed the Bush administration stance on cloning, nevertheless abstained in the vote, with its envoys saying it was necessary to have a consensus on the issue.
James Cunningham, the US deputy ambassador, said 100 nations backed Washington's position. Governments voting for a delay feared they would lose in a vote on substance, he said.
Anti-abortion groups want
President Bush to take action
"I think the desire for a delay is evidence that the countries supporting only a partial ban realised their position was eroding," he said after the vote.
As part of a fierce lobbying campaign on both sides, anti-abortion activists distributed photos of foetuses and pamphlets on genetic engineering to back their appeals for a total ban, while scientific groups flooded UN missions with e-mails and petitions in favour of a narrower treaty.
In debate before the vote, Iranian envoy Mustafa Dolatyar said the Islamic nations' motion was not meant to take sides on the issue but to reflect the lack of a consensus.
But Spanish diplomat Ana Maria Menendez argued it was a mistake "to send the international community the message that we have not proved capable of reflecting about this and taking a position during this lapse of time."
Nigerian envoy Felix Awanbor said his country backed a ban on stem cell studies for fear African women were "most likely to be at risk as easy targets to source the billions of embryos required for scientific experimentation on this issue."