(For a Factbox of regional efforts, click [ID:nN26348293])

* States to help with EPA efforts, federal auctions

* States, regions group to support bill when hits Senate

By Timothy Gardner and Peter Henderson

NEW YORK/SAN FRANCISCO, June 26 (Reuters) - States that have set the U.S. agenda on addressing greenhouse gas emissions are lining up behind a federal climate bill, fearing signs of dissent would weaken a plan with several hurdles left to jump.

Nearly half the U.S. states have moved toward curbing greenhouse gas emissions and want the federal government to learn from their experience in creating systems to cap emissions and trade pollution credits.

The U.S. House of Representatives on Friday was considering a climate change bill, widely known as Waxman-Markey after its sponsors, that would create a national system to cap greenhouse gas emissions and allow trade of such credits.

The government would issue a declining number of permits to companies, which could sell them to each other as needed, and carbon emission would drop 17 percent by 2020 and 83 percent by 2050, from 2005 levels.

Supporters hail it as the first substantial national step to ease global warming. Republicans in Congress have attacked the legislation, saying it would increase consumer prices as companies are forced to switch to more expensive alternative fuels. The bill's future in the Senate is uncertain this year.