BONN, Germany - Efforts to limit global warming must move into a new phase this year or risk a breakdown that would hurt poor countries threatened most by climate change, says the UN's top climate official.

Delegates from 166 countries began a second week of talks in Germany on Monday to prepare for a decisive meeting in December intended to launch negotiations on a new set of rules for controlling greenhouse gas emissions.

The new accord would succeed the Kyoto Protocol, which ends in 2012 and calls on 35 industrial countries to reduce emissions of carbon dioxide by an average 5 percent from 1990 levels. Developing countries benefit because the industrial countries earn credit by sponsoring green projects that reduce their emissions.

Experts say negotiations on the post-2012 agreement are expected to take at least two years, and should begin this year to avoid any gap between Kyoto and the new regime.

The Bonn meeting of nearly 2,000 delegates is aimed at drafting texts on technical issues and "clearing the brushwood" ahead of December's meeting on the Indonesian island of Bali, said Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change.

But at Bali nations must come to grips with the tougher political issues: how to involve the United States, which has rejected the Kyoto process, and how to bring in big developing countries like China, India and Brazil, major polluters which were excluded from Kyoto's mandatory commitments.

Failure to resolve these problems and to begin a new round of formal negotiations would be a setback for the credibility of the multinational process, De Boer told The Associated Press over the weekend.

"If Bali stalemates, we would see disintegration. This process is the only one that brings together all the players and all of their interests, and seeks to unify them in a common direction," he said.

The European Union would go ahead with its aggressive plan to reduce emissions by at least 20 percent by 2020, and other industrial countries would probably continue with their own measures to fight climate change, he said. But developing countries would suffer from the fragmented approach.

"I would expect issues like technical transfers, capacity building and helping developing countries adapt to climate change to be completely off the table, since those are integral to a multinational process," de Boer said.

Developing countries made it clear at the Bonn meeting they need more help and funding for new technologies and to build a modern infrastructure so they can better control carbon emissions without slowing their expanding economies.

Delegates have raised several ideas to encourage countries like China to participate. Under one plan, such nations would be rewarded for meeting accepted emissions targets but -- unlike industrialized countries -- would not be penalized if they fell short.