Downturn no reason to delay climate pact - expert

* Delay will raise cost of cutting greenhouse gases

* Climate talks hinge on developing countries

By Doug Palmer

WASHINGTON, March 4 (Reuters) - Countries will face an even harder job of cutting greenhouse gas emissions if they delay reaching a deal this year because of the global economic downturn, a British climate change expert said on Wednesday.

"Putting things off in this area is really costly," Nicholas Stern, a former British Treasury economist said in a speech at the Peterson Institute for International Economics.

Each year countries postpone an agreement, greenhouse gases will continue to rise, Stern said.

"If you wait for five years before you get going ... you're at a much more difficult starting point," Stern said. "We have to show people that high carbon growth within a few decades becomes a contradiction in terms. It kills itself."

Stern released a seminal report in 2006 that warned that inaction on emissions blamed for global warming could cause economic pain equal to the Great Depression of the 1930s.

But with many countries already in the midst of a tough recession, some question if now is the time for new climate change commitments that would raise business costs.