By Alister Doyle and Stian Reklev

DOHA (Reuters) - The United States resisted pledging steeper cuts in greenhouse gas emissions by 2020 on Monday despite calls by poor nations at the start of a U.N conference for tougher action to avert storms, droughts and rising seas.

About 200 nations met for annual U.N. talks on global warming with little prospect of a breakthrough and recriminations over how to keep alive hopes of a new, global U.N. deal to fight climate change meant to start up in 2020.

"We're sleepwalking off a cliff," Alden Meyer of the Union of Concerned Scientists said. There was a lack of ambition to confront rising world greenhouse gas emissions at the two-week meeting, the first in an OPEC nation, he said.

U.S. deputy climate envoy Jonathan Pershing said that President Barack Obama was sticking to his 2009 goal of cutting emissions by 17 percent below 2005 levels by 2020. That target was not approved by the U.S. Senate.

"I do not anticipate that the United States will modify the commitment we have made," he told a news conference. Washington was taking aggressive action to cut emissions and its national emissions may have peaked, he said.

Obama has said that he will focus more on climate change in his second term.

China's chief delegate Su Wei insisted that the rich should extend the U.N.'s Kyoto Protocol, the existing plan that binds developed nations to cut emissions by at least 5.2 percent below 1990 levels between 2008 and 2012.

"If there is not agreement on a second commitment period of the Kyoto Protocol ... I think that would be disastrous for talks on future enhanced action after 2020," he said, referring to plans for a global U.N. pact meant to be agreed by 2015.

"If we cannot agree on immediate actions, how can anyone agree on future actions?" he said, urging the rich to do more.

UNIMAGINABLE SCALE

A group of more than 100 developing nations also said developed countries should do more to avoid damage on a "previously unimaginable scale".

China has overtaken the United States as the top emitter, ahead of India and Russia.

The European Union has also said that it has no plans to increase its goal for cutting emissions, to 20 percent below 1990 levels by 2020, in Doha. The U.S. goal corresponds to a cut of 3-4 percent below 1990 levels by 2020.

Pershing said that extreme weather, including Superstorm Sandy and widespread droughts in the United States "are certainly changing the minds of Americans" who have often been sceptical about the need for more action on climate change.

A U.N. study last week said the world was on target for a rise in temperatures of between 3 and 5 degrees Celsius (5.4 to 9F) because of increasing emissions.

A U.N. conference two years ago agreed to limit any rise in temperatures to below 2 degrees Celsius (3.6F) above pre-industrial times. But greenhouse gas levels hit a new record in 2011, despite the world economic slowdown. Continued...