UPDATE 1-France, Germany urge more flexible climate pact

* Suggest rich guarantee overall 2020 greenhouse gas cuts

* Would allow U.S. to catch up later (Recasts, updates with French/German idea)

By Alister Doyle, Environment Correspondent

PARIS, May 25 (Reuters) - France and Germany suggested on Monday that rich nations should collectively guarantee deep cuts in greenhouse gases by 2020 while giving flexibility to laggards such as the United States to catch up later.

France said the idea, floated at talks among 17 top greenhouse gas emitters including China, United States, Russia and India, could help towards a new U.N. climate treaty due to be agreed at a meeting in Copenhagen in December.

"There can be more flexibility among us," French Environment Minister Jean-Louis Borloo told a news conference on the first day of the two-day talks among ministers, called by U.S. President Barack Obama to help work out a new climate treaty.

He said France and Germany reckoned that developed nations could collectively sign up to cut their overall emissions by 25 to 40 percent below 1990 levels by 2020 -- the level outlined by a panel of U.N. scientists to avoid the worst of global warming.

"There may be some who act faster and others who do more later," he said. A collective goal would undercut criticisms by developing nations, led by China and India, that the rich are not serious in fighting climate change.

Countries which have said they cannot reach such deep 2020 goals, led by the United States, could contribute to a new pact in other ways, for instance via a bigger share of financing or green technologies for developing nations, Borloo said.