Four environmental groups sued the Bush administration Tuesday to block changes that would allow more people to ride snowmobiles in Yellowstone and Grand Teton national parks.

The lawsuit, filed in U.S. District Court, asks a federal judge to block an Interior Department decision to reverse a Clinton administration ban on snowmobiles in the parks by next winter.

Under the Interior Department proposal, no limits would be placed on snowmobiles this winter, and starting next winter, no more than 1,100 snowmobiles a day would be allowed in the parks and a portion of the John D. Rockefeller Jr. Memorial Parkway connecting them.

The parks have had an average of 840 snowmobiles daily during the winter but up to 1,650 a day during holiday and other busy weekends for the past decade, meaning the new rules would allow more snowmobiles in the parks on average while cutting numbers on the busiest days.

The parks are in northwestern Wyoming. Yellowstone also extends into Idaho and Montana, from where most snowmobilers enter the park.

Public Employees for Environmental Responsibility, the Fund for Animals, the Bluewater Network and the Ecology Center filed the lawsuit.

They argue that snowmobiles pollute the park, create unacceptable noise and endanger the health of Yellowstone workers stationed at park entrances.