Thirteen steamships that ply the Great Lakes would be exempted from EPA air pollution rules under a policy rider in the 2010 Interior-Environment spending bill, an environmental group said Tuesday.

The EPA also would have to work out an agreement that would allow operators of 40 diesel-burning steamships to plead economic hardship to gain more time to switch to cleaner-burning fuel, Clean Air Watch said.

The language by House Appropriations Chairman David R. Obey , D-Wis., is expected to be ratified Tuesday afternoon, when House and Senate conferees meet on the fiscal 2010 Interior-Environment appropriations bill.

The issue has been a concern for Obey and several Great Lakes lawmakers, including James L. Oberstar , D-Minn., chairman of the House Transportation and Infrastructure Committee.

Under a proposed EPA rule, emissions from new marine compression-ignition engines operating at or above 30 liters per cylinder would be regulated. The Interior-Environment bill would exempt 13 ships from that rule.

During the comment period that ended Sept. 28, the Lake Carriers Association and Propeller Club of the United States opposed the rule. The Propeller Club warned in its comments that the proposal “could potentially cripple the shipping capacity and the entire maritime industry along the Great Lakes-Saint Lawrence Seaway.”

Environmental groups have opposed any efforts to restrict EPA’s ability to reduce air pollution.

Frank O’Donnell of Clean Air Watch said excluding the 13 oldest ships, one reportedly 103 years old, means continued pollution for the Great Lakes region.