Wyoming sued the federal government Friday over a Yellowstone National Park plan that would reduce the number of snowmobiles allowed per day from 720 to 318 this winter.

The suit claims that federal officials ignored science, violated the National Environ-mental Policy Act and the U.S. Constitution, among other laws, in forming the plan. Wyoming Attorney General Bruce Salzburg filed the lawsuit in U.S. District Court in Cheyenne after Yellowstone and Grand Teton National Park published snowmobile rules in the Federal Register.

The lawsuit also applies to Grand Teton’s permanent plan, which allows limited access to Jackson Lake and Grassy Lake Road.

“There is a line where access to the parks becomes so restricted that the mandates of the very legislation establishing the National Park Service and Yellowstone National Park are violated,” the suit states. “The 2009 winter use plans, which limit daily snowmobile entries into Yellowstone National Park to 318 per day, and which essentially eliminate snowmobile access to Grand Teton National Park, cross that line.”

The court documents say the Park Service implemented the plan “in spite of the clear scientific evidence demonstrating that the environmental impacts of snowmobiles in the parks are less than the impacts of snow coaches and that the entry of greater numbers of snowmobiles in the last four years has not resulted in any harm to the parks.”

“There is no rational basis to discriminate against snowmobiles in this fashion and no rational explanation for the disparity between the two modes of transportation,” the documents say.

The lawsuit requests that the judge vacate both Yellowstone and Grand Teton’s plans and revert back to a 2004 rule that allows 720 snowmobiles and 78 snow coaches a day in Yellowstone. The Park Service contends that fewer snowmobiles results in less environmental impact on Yellowstone, while conservationists have argued that science supports a total snowmobile ban.

Wyoming Gov. Dave Freudenthal said the lawsuit is necessary.

“This policy continues the Park Service’s unacceptable pattern of limiting public access to the public’s lands,” Freudenthal said. “This rule fails the eyeball test. The Park Service itself has determined a significantly higher number of snowmobiles can be allowed into the park without harm, but yet they settle on 318 a day.

“We all agree Yellowstone needs to be protected. But what the Park Service is proposing is incompatible with its own findings,” the governor said.

The interim rule would allow 318 snowmobiles and 78 snow coaches per day for the 2009-10 and 2010-11 winter seasons while the Park Service comes up with a permanent plan. The interim plan would include 114 snowmobiles and 13 snow coaches a day through the park’s South Entrance, which provides access from Grand Teton National Park and Jackson Hole.

Yellowstone spokesman Al Nash said the interim rule is “an important step that we needed to take in order to open as scheduled less than a month from now for winter.”

Louise Lasley, public lands director for the Jackson Hole Conservation Alliance, said a snow coach-only alternative would better protect park resources.

“We believe that the National Park Service should continue requiring best available technology and, more importantly, guided services for visitors to the park in the winter,” she said. “It is our understanding that these two requirements have greatly diminished the impacts on wildlife in Yellowstone. For that progress to continue and further diminish impacts on wildlife, we would prefer the visitor use of snow coaches and the phaseout of snowmobiles.”