WASHINGTON — The U.S. aviation industry has cut its greenhouse gas emissions by 13 percent since 2000, even as the amount of flying has reached record levels, government data show.

The decline was among the steepest of any sector measured by the Environmental Protection Agency and came as total U.S. emissions of gases that warm the Earth remained level between 2000 and 2006. Greenhouse gases from cars and trucks rose 6 percent in that period, according to an EPA report in April.

Aviation has faced pressure to improve efficiency as fuel prices began soaring in 2003. More recently, elected officials and environmentalists have called for stricter controls on aircraft emissions, particularly carbon dioxide, the most prominent greenhouse gas.

Airlines cut fuel consumption from a record 20.4 billion gallons in 2000 to 19.6 billion in 2006, Department of Transportation figures show. In that period, their planes flew 18 percent more miles on domestic and international routes. That marks the first extended period in which airlines have cut fuel use while flying more miles, DOT data show.

"The airlines have historically done a much better job than the auto companies at increasing efficiency," said Deron Lovaas of the Natural Resources Defense Council. "They feel fuel prices much more than your average consumer feels changes in fuel costs at the pump."

Airlines have taken many steps to curb fuel use, such as adding navigation equipment so planes can fly more direct routes, modifying wings to improve aerodynamics and shaving weight from jets by installing lighter seats. Older jets are being replaced with newer, more fuel-efficient models.

Plane efficiency — the amount of fuel consumed per mile flown — improved by 23 percent from 2000 to 2006, DOT figures show. Auto efficiency rose by 2 percent in that time. Commercial planes account for 2 percent of U.S. greenhouse gas emissions.

Industry officials warn that aviation's improvement may be hard to continue.

"There's so little left you can do other than renewing the fleet or flying less," said John Heimlich, chief economist of the Air Transport Association.