Poznan, Poland - Reaching a global climate deal by the end of next year will be difficult, even with Barack Obama as US president, the top US envoy at UN negotiations said Monday.

Harlan Watson, a State Department official representing the Bush administration at global warming talks in Poland, also said he expects no agreement on target dates for specific cuts in greenhouse gases to emerge from the two-week conference.

US officials were in an awkward position at the 190-nation talks, pledging to negotiate constructively while everyone else waits for Obama to re-energize US climate policy after taking office on January 20.

Watson said he believes Obama will find it hard to balance competing regional interests in the United States when he seeks to rally lawmakers behind targets for cutting greenhouse-gas pollution and an emissions trading system.

"It's not a partisan issue," he told reporters. "It is a difficult issue. I don't think anyone expects it to be done soon."

Under a tight timeline agreed last year by world governments including the United States, UN talks to combat global warming are scheduled to wrap up by next December with a global deal to cut back on carbon dioxide emissions.

That means Obama will be in charge in Washington during the toughest part of negotiations, which are expected to include limits for developing countries for the first time.

"That's what we've agreed to," Watson said of the deadline. "It won't be easy."