The 171-member Convention on International Trade in Endangered Species, or CITES, approved the deal by consensus, in what Europe hailed as a milestone for the wildlife trade organization.
The arrangement allows South Africa, Namibia, Botswana and Zimbabwe to empty government inventories in a single sale to Japan. But future sales will be frozen for nine years after the sale goes through.
Critics of the sale came to the conference demanding a 20-year moratorium on reopening the ivory ban for discussion.
The dispute over the ivory sale consumed the energies of the two-week conference by CITES, which sets the rules for wildlife commerce and regulates the trade in tens of thousands of plants and animals.
Conservationists gave the agreement a cautious welcome, saying it provided a nine-year reprieve for elephants but could stimulate poaching and an already lively illegal market.
"It will excite a demand that can never be supplied by legal sources. It will encourage the illegal market, and that's what kills elephants,' said Michael Wamithi, the Kenya-based elephant expert for the International Fund for Animal Welfare.
The United States objected to the inclusion of Zimbabwe, accusing the government of complicity in the illegal ivory trade and charging that more than 900 poaching camps have been found on its territory — six times more that were found in 2001. But chief delegate Todd Willens said the United States would not try to amend or block the compromise.
However, TRAFFIC, an independent group monitoring the movement of wildlife products, said it looked into the claims of Zimbabwe complicity and found none.
Last week, CITES cleared the way for Botswana, Namibia and South Africa to sell 60 metric tons of ivory, as agreed in principle at the last conference in 2004.
But the three countries, joined by Zimbabwe, came to this year's conference with a proposal that would scrap the ban on ivory sales imposed in 1989 — a time when Africa's elephant herds were being decimated for their tusks and risked extinction.
Kenya and Mali countered with a proposal for a 20-year moratorium.
Negotiations on a compromise document lasted until nearly 3 a.m. Thursday after CITES repeatedly postponed votes on the competing proposals.
"This is really a great day for the elephants," said Germany's chief delegate Jochen Flasbarth in an interview. "When I came here I never expected such a super response."
Flasbarth, who led the mediation, told the conference the compromise was "a milestone for the convention" in what he said was its act of peacemaking between rival states.
The final document did not specify how much ivory would be released. But in a key compromise by the southern Africans, it said the four countries could sell their inventories as verified by CITES as of Jan. 31, 2007. The amount would be far less than the 200 tons proposed in an earlier draft by the European Union.
The International Fund for Animal Welfare estimated the total amount held by three countries was 60 metric tons, and Zimbabwe said it also held about 10 tons.
"We are fairly happy," said Francis Nhema, Zimbabwe's minister of environment and tourism.
Nhema said fears of poaching in his country were exaggerated when compared with the number of elephants in Zimbabwe's savannah.
"We have a population of 100,000 or so and in the last year we lost about 100," he said.