NEW YORK - Five states have asked U.S. Senate leaders to let them impose stricter limits on greenhouse gas emissions than what would be permitted under the climate legislation working its way though Congress, saying both levels of regulation are necessary to fight global warming.

The climate bill the House of Representatives narrowly passed in June would preempt statewide caps on greenhouse gases, while cutting total U.S. emissions by 17 percent from 2005 levels by 2020.

Senate leaders will reveal their version of the bill later this month and hope to vote on it later in the year.

The group of attorneys general, which includes Edmund Brown of California, Richard Blumenthal of Connecticut, and Anne Milgram of New Jersey, opposed limits on their ability to regulate the emissions, which they formed in the absence of federal climate regulations during the administration of former U.S. President George W. Bush.

States should continue to be able to adopt caps that are more stringent than federal requirements in order to ensure that the ambitious targets set by the act, and required to avoid disruptive climate change, are met, the attorneys general wrote in a letter obtained by Reuters.

They had sent the letter on Monday to Senate leaders including Democrats Harry Reid and Barbara Boxer, and Republicans Mitch McConnell and James Inhofe.

The House version of the bill would preempt state caps on greenhouse gas emissions from 2012 to 2017.

That would effectively halt the Regional Greenhouse Gas Initiative, a group of 10 states in the East, from carrying out their cap-and-trade market that launched in January. Those states cap carbon dioxide emissions from power plants. The group has raised nearly $370 million for clean energy and efficiency funds by selling emission permits in quarterly auctions.

It would also preempt the Western Climate initiative that would covers six greenhouse gases across 11 U.S. states and Canadian provinces from launching in 2012.

The targets of both regional plans are weaker than those in the climate bill. But leaders in the states have said they would like the option to ratchet up their plans once a federal system kicked in.

The states also called on the Senate to strengthen the bill by pushing the reduction target up to 20 percent by 2020 from 2005 levels in order to better fight climate change.

The other attorneys general that wrote the letter were Terry Goddard of Arizona and Joseph Biden III of Delaware.