(Adds U.S., U.N. quotes, details)

By Alister Doyle, Environment Correspondent

VIENNA, Aug 27 (Reuters) - Climate negotiators from more than 150 nations sought a global deal beyond 2012 on Monday to widen the U.N.'s Kyoto Protocol to include outsiders such as the United States and China.

"Climate change is already a harsh reality, a massive obstacle to development," Austrian Environment Minister Josef Proell told the meeting in Vienna of more than 1,000 senior officials, activists and other experts.

"Climate change is a huge challenge that can only be dealt with at a global level," he said. "We do not have much time."

Activists from Greenpeace, who say that world climate talks advance at a glacial pace, demonstrated outside the conference hall with a big yellow balloon. Activists, their heads disguised as giant eyeballs, said: "the world is watching."

The Aug. 27-31 Vienna meeting is meant to pave the way for a deal among environment ministers who will meet in December in Bali, Indonesia, to launch formal 2-year talks on a broader successor to Kyoto, which binds 35 industrial nations to cut emissions by 5 percent below 1990 levels by 2008-12.

The United States, the top emitter of greenhouse gases from burning fossil fuels, is not part of Kyoto. President George W. Bush has said that Kyoto was too costly and wrongly excluded 2012 targets for developing nations such as China and India.

But Bush has signalled willingness to join in negotiating a new, long-term worldwide U.N. pact and has called a meeting of major emitters for Sept. 27-28 in Washington.

"The results will feed into the U.N. process," said Harlan Watson, the chief U.N. climate negotiator, rejecting worries by some delegates that Bush's plan meant a rival track.

MOMENTUM

Yvo de Boer, the U.N.'s top climate change official, said there were "many encouraging political signals building momentum for action on climate change" in recent months.

"Bush has taken the bull by the horns and the question now is where will Mr. Bush and the bull go?" he asked.

U.N. reports this year have blamed humans for global warming over the past 50 years and forecast worsening disruptions from floods, droughts, heat waves and rising seas.

The Vienna talks will also review a U.N. report showing that additional investments and financial flows of $200-210 billion will be needed in 2030 to return greenhouse gas emissions to current levels.

And de Boer defended developing nations such as China and India from criticisms that they are doing too little to rein in their surging emissions. "There's this myth out there that developing countries are doing nothing," he said.

He said, for instance, that China had promised to improve its industrial energy efficiency by 20 percent in the next five years and improve recycling even as it opens coal-fired power plants at a rate of two a week to feed its growing economy.

Proell, the Austrian host, pointed to monsoons in South Asia and fires in tinder-dry Greek forests as signs of the type of weather that might become more frequent in future.

Kyoto backers will also start discussing targets for long-term cuts. The European Union has already said it will cut by 20 percent below 1990 levels by 2020.

"For the first time we'll start to talk about specific numbers," said Leon Charles, from Grenada, who heads a group looking into new cuts by Kyoto backers.

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