"It's just like a postcard, isn't it honey?" Bobby Patterson sighed to his wife, Pam, as they watched a winter herd of bison forage beside the Firehole River as steamy geysers erupted in the snowy distance.

Then they heard the whine.

Distant at first, like monster mosquitoes, then louder, blatting, finally screeching, as a pack of 14 snowmobilers came sledding into view. Astride their rumbling Arctic Cats and Ski-Doos, swaddled in snowsuits and helmets, they looked like middle-aged road warriors from a "Mad Max" sequel.

"You know, I love riding in the park," said Patterson, a construction engineer from Sioux City, Iowa, who had arrived at this spot upon his rented Polaris sled. Above the din, he shouted, "But you got to admit, we're a little bit obnoxious."

The Snowmobile War of Yellowstone has flared again, and it is one of those elemental environmental conundrums that pit Americansagainst each other, in competing visions of how the nation's premier parks should be run.

Here, it's essentially the birdwatchers against the NASCAR crowd -- and these clashes have, in turn, broken down along party lines in Washington.

Faced with images of park rangers wearing gas masks gasping at the West Gate (which could see 1,000 sleds arrive on a busy holiday) and hot-dogging snowmobilers herding (and harassing, the biologists say) bison through a smoggy haze, the Clinton administration in its last days ordered the machines banned from Yellowstone beginning next winter.

The machines, essentially motor bikes on skis that can rocket along at speeds of 60 or 70 mph, "are just not an appropriate means of enjoying Yellowstone in the winter," said Don Barry, the former assistant secretary at the Interior Department who spearheaded the ban and is now a vice president at the Wilderness Society. "But try telling that to the boosters, who believe the more the merrier."

The snowmobile industry and its enthusiasts rallied, and the Bush administration recently announced its intent to reverse the Clinton-era order and to allow the sleds into Yellowstone -- though with caps on numbers admitted and requirements that the sleds be "cleaner and quieter." It's a move the administration describes as a common-sense compromise that allows continued access to the park while mitigating pollution and harassment of wildlife. A final decision is due in March.

Unless there is an intense backlash, the National Park Service has decided that it will allow the sleds continued entry into Yellowstone, even though the agency's impact studies (which are officially under wraps but have been circulating for months) conclude that "the environmentally preferred" alternative is to ban the machines.

"I wouldn't say we're happy, but we're just glad we're still allowed in the park; that's the important thing," said Jack Welch, president of the Blue Ribbon Coalition. It's an advocacy group that defends the rights of off-road enthusiasts, whose use of jet skis, swamp buggies, ATVs and snowmobiles on federal waterways and parks has been the subject of ongoing controversies from the Florida Keys to the California sand dunes.

The anti-snowmobile forces are crying sellout. Lawsuits are almost inevitable once a decision allowing the machines into the park is signed.

The Snowmobile War is emotional and filled with battles over images, economics and science. There were more than 350,000 letters sent to the Park Service about the ban. More than 80 percent favored keeping snowmobiles out of the park.

The debate, though, is something of a culture clash, and it swivels on a most ephemeral question: What is the value of quiet -- or, as park officials call it, "the soundscape," meaning how to quantify and qualify a visitor's right to hear wind in the pines, the riffle of a river and the creak of an eagle wing -- against the white noise of snowmobile traffic.

The snowmobile enthusiasts acknowledge that their machines are noisy, and many interviewed in the park agree that their numbers should be controlled and that within Yellowstone, they should be driven more like golf carts than motocross bikes. But they also ask why snowmobiles should be banned without doing something about the 1 million automobiles that jam the park each summer.

"If we're banned from the park, they're taking away my right to bring my kids here someday, to show them Yellowstone in the wintertime," said Jeff Vigeant, who works for a tool and industrial supply company in the Boston area. He was here on an annual trip with friends.

The Clinton team wanted Vigeant and his kids to enter the park in "snow coaches," which are akin to 10-passenger vans propelled by treads and operated by hired drivers. But snowmobilers hate them.

"I wouldn't go to the park in a snow coach," said Wayne Dieter, an auto parts distributor from Minnesota on his sixth trip to Yellowstone. He called the vans "snow couches." "They smell. They're old. They're slow. And you're trapped with a busload of senior citizens."

Indeed, snow coaches are not very popular. Three out of four people who visit Yellowstone in winter arrive astride a snowmobile. Only 1 in 10 boards a snow coach. And only a few hundred people -- out of 140,000 wintertime visitors -- ski into the park (though more visitors ski cross-country after they've come in on snowmobiles or coaches). But environmentalists (and park officials under Clinton) argued that a new generation of snow coaches could entice more riders.

Older snowmobiles can be dirty and loud, belching headache-inducing benzenes and formaldehydes and carbon monoxide. Powered by two-stroke engines, the machines are quick and strong (and painted bright red with names like the "Firecat"), but they burn fuel inefficiently, discharging fumes and oil.

"They're for hot-dogging around," Clyde Seeley, who operates a fleet of 260 rental snowmobiles, said of the two-stroke sleds. But the latest machines are powered by four-stroke engines that are much quieter and cleaner, producing 95 percent less hydrocarbons and operating at decibel levels that are more like a loud argument than a hysterical scream.

"I think the new technologies will save us," Seeley said. "The machines will get quieter and cleaner each year, just like cars." Seeley said he could envision a future fleet of snowmobiles designed for national parks that would be slower and more comfortable, and outfitted with anti-pollution devices.

He and other boosters stressed that snowmobiles are the ideal freedom machines to use in the parks, where roads this time of year are virtually impassable to cars. Snowmobile riders can stop wherever and whenever they want. "Without snowmobiles, who is going into the park? The answer is nobody. And that would be a shame," Seeley said.

Riding a new model four-stroke through Yellowstone is a relatively tame experience these days, compared with the Wild West raceway of smoky two-strokes bombing around outside the park. The new sleds are big and comfortable, with electric starters and hand-warmers, and wide seats as comfortable as a La-Z-Boy recliner.

Over the Martin Luther King Jr. holiday weekend, many of the thousands of snowmobiles in the park were the four-stroke models. They were restricted to the same roads used in the summer by the 1 million cars that cruise the park each year. Going cross-country or on trails is forbidden to snowmobilers, and every few miles, there was a ranger beside the road, enforcing the 35-mph speed limit like traffic cops with a radar gun.

The machines and their riders are sometimes guilty of harassing the wildlife, especially vulnerable during the winter. Biologists have recorded elevated levels of stress hormones in bison, but they have also noted that elk appear to be more fearful of a cross-country skier than a pack of snowmobilers.

Under the Bush administration proposal, which would kick in next winter, most of the snowmobilers would be required to hire a guide, and park officials see this as a crucial compromise. "We think the guides are fundamental to controlling the issue of inappropriate behavior," said John Sacklin, chief of planning and compliance at the park. He describes the new approach as "managing snowmobilers rather than simply banning them."

"Look, we're not yahoos; we're reasonable people. We've got families and jobs and we're responsible. I'd call myself an environmentalist," said Jim Grogan, a real estate agent from Florida. "We agree. Make us obey the speed limits. Put us on the new sleds with quiet engines. But, really, don't even think about banning us from the park. That is extreme."

Anne Carter is not so sure. The Minnesota accountant was cross-country skiing along a trail beside Old Faithful and said, "You hear the snowmobiles all day long. Buzz. Buzz. Buzz. It's like a race track. Why don't these people get off those things and really see the park? It could be so" -- she paused -- "peaceful. But I guess that's not the American way. We love our machines."

Asked how she got into the park, Carter laughed and said, "I came in on a snowmobile."

Californians Hans and Teresa Nettel, with their dog, Prince, park their snowmobile Monday at Yellowstone National Park. The Park Service plans to impose new limits on the number and type of snowmobiles allowed in the park.