WASHINGTON – Federal appeals court judges upheld tougher pollution controls on snowmobiles Tuesday but asked why the Environmental Protection Agency rule would exempt almost a third of newly built snowmobiles.

A three-judge panel of the U.S. Court of Appeals for the District of Columbia rejected claims by the snowmobile industry that the EPA had no authority to require new snowmobiles to have cleaner-burning engines to reduce air pollution.

The ruling came in a lawsuit filed by two environmental groups that argued the 2002 EPA rule requiring new snowmobiles to have on average a 50 percent reduction in tailpipe emissions by 2012 was too lenient.

The EPA acknowledged it had written the regulation in such a way that manufacturers would not have to equip about 30 percent of their snowmobiles with cleaner engines. The industry said to require 100 percent compliance would be too costly and force manufacturers to stop making certain models.