BOISE - Early-season snow just dusts the peaks above Idaho's capital, but a courtroom battle down in the valley could have a big impact on who gets to ride where on the accumulating white powder.

A backcountry skier advocacy group, the Idaho-based Winter Wildlands Alliance, will ask a federal judge today to force the U.S. Forest Service to create plans for snowmobiles limiting their travel on public land - a decision that would apply to national forests all over the country.

National forests since 2005 have been required to craft travel management plans restricting wheeled cross-country travel to designated routes. But snowmobiles were exempted, as the agency allowed individual national forests the freedom to decide if such winter travel plans were necessary.

Some forests created them, including the Clearwater National Forest in north central Idaho. Others, such as neighboring Nez Perce National Forest, begged off.

Absent any consistency, alliance director Mark Menlove speaks of tense outings in places like the Boise National Forest, where hordes of powerful motorized sleds unrestrained by a winter travel plan sometimes roar past panting groups of backcountry skiers, disturbing their icy, human-driven idyll.

"One snowmobile can track up an area in an hour that a dozen skiers could use for two weeks," said Menlove. "It is a competition for a limited resource. Beyond untracked powder, we also think that quiet is a forest resource that should be managed."

This dispute over snowmobile travel on national forests represents a broadening of a contentious fight in Yellowstone National Park, just over the border in Wyoming.

There, the number of snowmobiles allowed to enter the famed geyser-filled preserve every winter has been curtailed over the last decade, amid concerns over air quality and wildlife.

Not surprisingly, Idaho snowmobile groups have sided with the Forest Service in fighting Menlove's lawsuit, arguing it would be wasteful folly to require every U.S. national forest to craft its own plan for over-the-snow motorized travel.

With 193 million acres of national forests and grasslands, said Sandra Mitchell, a lobbyist for the Idaho Snowmobile Association, surely there's enough to go around for everybody - regardless of their mode of winter travel.

Mitchell, who prefers a Polaris 700 snow machine, said forced winter travel planning would be a poor use of precious taxpayer resources to solve a nonexistent problem.

"The Forest Service are the managers of the land," she said. "If they for a moment thought there needed to be winter travel management plans for every forest, they would do it. The money needs to go on the ground, not to do more planning if it's not needed."

A regional Forest Service spokeswoman, Erin O'Connor, declined to immediately comment on the litigation.

A phone call to U.S. Department of Justice attorneys handling the Forest Service's defense wasn't immediately returned.

But in court documents preceding Wednesday's hearing in Boise, Forest Service lawyers told U.S. Magistrate Judge Ronald Bush there's good reason why travel plans for snowmobiles weren't required alongside the plans being created under the 2005 rule to regulate where off-road vehicles could drive spring, summer and fall.

That rule, they argue, was clearly meant to target wheeled vehicles that many natural resource managers said were tearing up public land. Snowmobiles are simply different, the lawyers said.

"An over-snow vehicle ... results in different and less severe impacts on natural resource values than wheeled motor vehicles traveling over the ground," wrote assistant U.S. attorney Julie Thrower, asking Bush to reject Menlove's group's claims.

From his Boise office, Menlove counters his group - dubbed an advocate for "human-powered snow sport enthusiasts" - filed its federal lawsuit only as a last resort, after the Forest Service rejected its out-of-court bid to have the snowmobile exemption lifted.

"We're not saying snowmobiles don't have a place in winter," Menlove said. "They're a great tool and should be allowed, but they should be managed in the same fashion as any other off-road vehicle."