BILLINGS, Mont. — Moving to protect two of its crown jewels, the National Park Service said officially Wednesday that snowmobiles will be banned from Yellowstone and Grand Teton national parks over the next three years.

The Park Service had already limited recreational use of snowmobiles at nearly all of the national parks, recreational areas and monuments. Teton and Yellowstone, the nation's first park, had been exempt until now. The move was first announced a month ago.

Snowmobile use will be phased out beginning next year and will be banned by the winter of 2003, when the only motorized recreational access to the parks will be by snowcoach, Park Service regional director Karen Wade said. The coaches usually carry eight to 10 passengers.

The Park Service hopes the move will protect wildlife and the natural sights and sounds of the parks.

"This is a viable option, both economically and as a way to see the park," Yellowstone spokeswoman Marsha Karle said.

A study last year estimated that banning snowmobiles will cost the region $16.5 million and about 400 jobs. But other studies have documented environmental costs. Researchers from the Park Service issued a report last year that said snowmobiles produce nearly all the air pollution in Yellowstone. Snowmobiles emit 100 times as much carbon monoxide and 300 times as much hydrocarbons as do automobiles, according to the report.

More than 62,500 snowmobiles entered Yellowstone from last December to March, Karle said.

The ban is opposed by community leaders who fear a loss of business and politicians who criticized the government for restricting access to the two parks in northwestern Wyoming.

"Not to say we won't be able to see a way to make it work over time," said Fred Rice, the operations manager in West Yellowstone. "But, unfortunately, the mandated time frame . . . doesn't give us the flexibility we need."

There were also harsh words from the congressional delegations of Montana and Wyoming.

"Whether or not you are a snowmobile user, it is not overstating things to say that the recreational and use rights of everyone to access public lands are at stake when a federal agency makes no real effort to accommodate them," said Sen. Craig Thomas, R-Wyo.

GOP Sen. Conrad Burns of Montana said the Park Service "has chosen to ignore common sense, avoid public input and adopt a radical policy shift."

On the Net: Bluewater Network, supporter of ban:

BlueRibbon Coalition, opponent of ban:

National Parks Conservation Association: