* De Boer sees hundreds of billions needed in long term
* Climate chief says reports Copenhagen will fail "wrong"
UNITED NATIONS, Nov 19 (Reuters) - The U.N. environmental chief called on rich nations on Thursday to pledge $10 billion a year for three years at next month's Copenhagen summit to help poor states begin to tackle the impact of climate change.
Yvo de Boer, head of the U.N. Climate Change Secretariat, told a news conference that was a short-term figure and that in 10 or 20 years hundreds of billions of dollars would be needed annually to cope with global warming.
The Dec. 7-18 meeting in Copenhagen had long been billed as the time when a new treaty to cap greenhouse gas emissions would be signed, but the United Nations has admitted that a legally binding deal will not come until later.
The slippage has been partly blamed on delays in the United States in pushing new climate change legislation through Congress, a move now anticipated early next year.
De Boer listed the $10-billion-a-year pledge as one of his three goals for the summit, along with the submission of emission targets for 2020 by rich countries and of planned actions by developing countries.
He said Copenhagen must clarify how short- and long-term finance was going to be provided to help developing countries mitigate the effects of climate change and adapt to it.
"To my mind rich countries must put at least $10 billion on the table in Copenhagen to kick-start immediate action," he said.
"And they must list what each individual country will provide and how funds will be raised to deliver very large, stable and predictable finance into the future without having to constantly renegotiate the commitments every few years."
De Boer later made clear that he was talking about an annual $10 billion between 2010 and 2012.
"What I'm looking for is the prompt start-funding that can get us to solid plans, and on the basis of those solid plans calculate the long-term need and share the cost of that out amongst industrialized countries," he said.
Estimates have varied on how long it will take after the Copenhagen summit to get a deal finalized. De Boer repeated an earlier statement that he expected the details to be settled within six months, but later said he did not know if that would be possible.
He nevertheless struck a bullish tone for the summit, saying there was "no doubt in my mind whatsoever that it will yield a success. I've seen some recent reports that say that Copenhagen has failed even before it starts, and I must say that those reports are simply wrong." (Editing by Mohammad Zargham)
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