WASHINGTON - The U.S. economy will lose $2.4 trillion over the next two decades if the federal government does not allow oil and natural gas drilling in restricted onshore lands and in offshore areas previously closed to energy companies, according to a new study released on Monday.

The report, prepared for the National Association of Regulatory Utility Commissioners, also said U.S. imports of crude oil, petroleum products and natural gas would increase by $1.6 trillion over the period without access to the energy resources.

In particular, the United States is expected to pay the Organization of the Petroleum Exporting Countries (OPEC) $607 billion for an extra 4.1 billion barrels of crude, the report said.

Separate congressional and presidential bans on drilling in most U.S. waters beyond the western and central Gulf of Mexico ended in 2008, and the Interior Department is now considering whether to expand exploration in only a small part of the formerly closed areas.

"It's clear from this report that the status quo on energy production simply won't suffice," said David Parker, president of the American Gas Association. "We encourage lawmakers to heed the results of this study and take a closer look at the energy-rich areas in our country that are currently off limits."

Many environmental groups say the United States should rely less on oil and gas and more on cleaner energy sources like wind and solar.

The study also raised the estimated U.S. oil and gas resources that are available in all areas based on advance drilling technology and easier development of energy supplies trapped in shale rock.

As a result, U.S. resources of crude oil were increased by 43 billion barrels to 229 billion and natural gas was raised by 286 trillion cubic feet to 2,034 trillion cubic feet.