By Tom Doggett and Ayesha Rascoe

WASHINGTON (Reuters) - Climate change legislation passed by the U.S. House of Representatives would increase the energy costs of the average family by $142 a year in 2020 and by $583 in 2030, according to the government's top energy forecasting agency.

The estimate from the U.S. Energy Information Administration is in line with cost impact projections made by the Congressional Budget Office and the Environmental Protection Agency, and contradict claims by energy and business trade groups that consumers would pay thousands of dollars more a year under a government plan to fight global warming.

The EIA's estimate says gasoline prices would be 23 cents a gallon higher in 2020 and 36 cents more in 2030, according to a copy of the agency's analysis that was sent to U.S. lawmakers and obtained by Reuters.

Jeremy Symons, who oversees the National Wildlife Federation's climate change program, said the EIA's analysis shows that industry claims that efforts to fight global warming would significantly boost energy costs "are completely unfounded and simply scare tactics."

The EIA reviewed the impact of the climate change bill at the request of the House Energy and Commerce Committee. The agency sent its report to the panel, but has yet to make it public.

The House in June passed legislation to cut U.S. carbon emissions from utilities, manufacturers and others by 17 percent by 2020 and 83 percent by 2050, from 2005 levels.

The lower emission levels would be accomplished through a cap-and-trade system, where a U.S. company would be required to have a pollution permit to emit one ton of carbon dioxide and other greenhouse gas emissions each year.

Those companies that use cleaner energy and reduce their emissions could sell their permits to companies that pollute more.

The U.S. Senate is expected to unveil its climate change bill in September when lawmakers return from their summer recess.

(Reporting by Tom Doggett; editing by Jim Marshall)