(Corrects para 4 to "40 developed nations" from "40 developing nations")
* Ban says "perfect is the enemy of good"
* Rich-poor split over future of Kyoto Protocol
By Gerard Wynn and Timothy Gardner
CANCUN, Mexico, Dec 7 (Reuters) - United Nations Secretary-General Ban Ki-moon urged almost 200 nations meeting in Mexico on Tuesday to agree to a modest deal to rein in climate change without holding out for perfection.
After U.S. President Barack Obama and other leaders failed at last year's U.N. summit in Copenhagen to work out a sweeping new climate treaty, Ban stressed that Cancun has more modest ambitions.
"We cannot have a perfect agreement at this time ... perfect is the enemy of good," Ban said on the sidelines of the Nov. 29 to Dec. 10 talks in the Mexican resort of Cancun where ministers were meeting.
Rich and poor nations are deeply split about the future of the U.N.'s existing Kyoto Protocol, which obliges almost 40 developed nations to cut greenhouse gas emissions in a first period to 2012. Kyoto is blocking progress on other issues.
Ban said there were four areas being discussed where "we can make progress but we may not be able to make the full agreement."
The talks are seeking a four-way package on climate aid, ways to curb deforestation, help poor countries adapt to the impacts of climate change and a mechanism to share clean technologies.
Bolivia has led calls by some poor nations for deep cuts in greenhouse gases by rich nations that would require a radical overhaul of the world economy to help protect "Mother Earth."
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Many developed nations want emerging economies, led by fast-growing China and India, to do far more to rein in emissions, including greater oversight of their programs to limit rising greenhouse gas emissions.
"The negotiations are still difficult, a result is still possible," said U.S. climate envoy Todd Stern.
"The Kyoto Protocol issue continues to be very tough. It's not clear whether it's resolvable. I would certainly hope so," he said, adding that it was draining time from other talks.
Ban said he was concerned that the world had not done enough to rein in global warming, which a U.N. panel of climate scientists has predicted will cause more floods, droughts, desertification, heatwaves and rising sea levels.
Japan, Russia and Canada have been adamant that they will not approve an extension to Kyoto when the first period runs out in 2012. They want a new, broader treaty that will also bind emerging economies like China and India to act.
But developing states say rich nations have emitted most greenhouse gases since the Industrial Revolution and must extend Kyoto before poor countries can be expected to sign up.
Christiana Figueres, head of the U.N. Climate Change Secretariat, said the talks would have to find a compromise.
"We currently are still stuck on how parties are going to decide on the continuation of the Kyoto Protocol where we have diametrically opposed positions," she said.
"Germans have a wonderful word 'yein' which means both 'yes' and 'no' and I think that's the kind of attitude countries are now engaged in," she said. (Writing by Alister Doyle, editing by Christopher Wilson) For Reuters latest environment blogs, click on: http://blogs.reuters.com/environment/
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