NEW YORK - The federal government is considering modifying the way it calculates fuel-efficiency ratings for electric vehicles, a move that would likely reduce the miles-per-gallon claims that automakers have touted for their battery-powered cars, the Wall Street Journal reports.

Using a formula released by the Environmental Protection Agency (EPA), General Motors last year announced that its Chevy Volt would be rated at 230 miles per gallon in city driving, and Nissan said that its Leaf electric car would achieve the equivalent of 367 miles per gallon.

However, the agency is revising its formula to deliver more realistic mileage ratings, according to insiders familiar with the situation.

"We're working with EPA staff on testing of labels that will provide meaningful information to the consumer," said GM spokesman Greg Martin. "What we're finding is that the Volt and electric vehicles defy conventional mileage labels."

When projected mileage came out last year, the EPA said that the extent of skepticism and backlash took its agency by surprise. The mileage expectation reflected a new methodology for electric cars that factored in electricity to reach a miles-per-gallon equivalent. New figures will do the same, but the EPA is trying to devise a better way to compare electric power with gasoline.

The Department of Energy process cited by Nissan considers 82-kilowatt hours of electricity to be equivalent to the power generated by one gallon of gasoline.

Today, rather than touting a 230 miles-per-gallon capability for its Volt, GM is instead highlighting more tangible factors, noting that the car can drive 40 miles on a battery charge and when the engine kicks in, it will operate at roughly 50 miles per gallon.