To clean up the air in national parks and wilderness areas, U.S. EPA Administration Christie Todd Whitman this week may release for public comment a plan to require polluters to control emissions affecting parks. The proposal is based on one written by the Clinton administration, covering facilities ranging form power plants to smelters to pulp mills. Electric companies were vigorous opponents of the Clinton plan, saying it would be too expensive to implement. Meanwhile, 25 states have already exceeded clean-air standards at least once this year.