YELLOWSTONE NATIONAL PARK, MONT. -- Amid the geysers and buffalo herds of the Yellowstone plateau, two visions of the national parks are vying for preeminence.

One is the Yellowstone that nature built, where a visitor can wander through a landscape little changed since a member of the Lewis and Clark expedition strayed from his party and stumbled across its geothermal wonders in 1807.

The other is the recreational Yellowstone, where the same visitor can rent a motorboat or a snowmobile, rough it in a $95-a-night hotel and soak up many of its most famous sights without ever setting foot outside a car.

Arguments over the purpose of the national parks have raged since Yellowstone was created by an act of Congress in 1872, but lately the debate has taken on a new urgency. Record crowds, an aging population and growing state efforts to promote national parks as regional tourist attractions have intensified demand for creature comforts and services inside park boundaries.

At the same time, a newly powerful environmental movement is promoting its own definition of the parks, based heavily on the idea of nature for nature's sake. Environmentalists argue that in a rapidly developing world, the 50 national parks can play a vital role as reservoirs of biological diversity. And they are critical of the private concessionaires that run hotels, stores and restaurants within the parks, charging that profits too often take precedence over protection of natural resources.

"There's sort of a revolution of rising expectations," said Bob Barbee, Yellowstone's voluble superintendent. "You've got a coalition under every bush."

During the early 1980s, conservationists were horrified when then-Interior Secretary James G. Watt announced plans to boost the role of private entrepreneurs in the parks, but the controversy did not depart when he did. Battles over development have continued to erupt throughout the park system, from a proposed airport expansion in Wyoming's Grand Teton National Park to new snack stands and raft rentals at Yosemite.

Such conflicts are especially sharp at Yellowstone, one of the park system's "crown jewels" by virtue of its special status as the oldest national park and, at 2.2 million acres, the largest in the lower 48 states.

First-time visitors may be surprised at the extent of commercial development in Yellowstone, scattered through the park's broad plateau in nine distinct villages. There are several grand hotels, innumerable campgrounds and cabins, five full-service restaurants and a dozen fast-food shops, grocery stores and gift shops.

Nor is there any shortage of customers. Some 263 million visitors are expected at the 356-unit park system this year, a new record, and Yellowstone gets more than its share. Spurred in part by curiosity about the effects of massive fires in 1988, about 2.7 million people will visit the park this year, crowding roads and campsites to capacity.

Beyond sheer numbers, shifting demographics have placed new demands on park facilities and managers. Park Service research suggests that visitors are growing older, have more discretionary income and are more environmentally aware than in the past. They also take shorter trips and show "a growing desire for intense and meaningful recreation opportunities," according to one study.

The average stay at Yellowstone is just 2.5 days. Indeed, most people see the park "at 40 miles an hour," in the words of ranger Don Buss, with few of them venturing more than a short walk from paved surfaces.

Older visitors mean that the number of people interested in hiking to remote, backcountry areas is declining even as overall numbers rise. Yellowstone chief researcher John Varley said backcountry use went through a "free fall" in the late 1980s as "the baby boomers left their backpacks at home and started making hotel reservations."

As income grows, so do visitors' demands. "Twenty percent of our rooms in this park are without baths, and they're the last ones to sell," said Steve Tedder, general manager for TW Recreational Services Inc., which runs Yellowstone's hotels and restaurants. At one location, a string quartet entertains guests as they wait for tables, generating "tons" of approving comments, Tedder said.

Also driving the push to upgrade facilities in and around the park are state tourist boards in Montana and Wyoming, which regularly pitch Yellowstone in publications such as Sunset and Readers' Digest. Environmentalists fret that such marketing efforts will only create new demand, a worry that Barbee says he shares.

"I always remind my friends in the travel and tourism industry, 'Let's not diminish the kinds of things you're trying to capitalize on,' " he said.

But solitude is never more than a short hike away, and most visitors seem pleased by what they find. "I think it's wonderful," said Lynne Crumpacker, a potter from Edinburg, Va.

She and a companion, Jack Troy, had paused in their van at daybreak recently to watch buffalo graze in the meadow at Hayden Valley, and they did not seem bothered by the fact that dozens of others had done the same -- creating one of Yellowstone's infamous "buffalo jams."

"When you get up early and you see animals like this, you realize you're in a real special part of the planet," said Troy.

Much of the current debate is rooted in the past. Established in 1916, the Park Service was a heavy promoter of development, building roads and offering free land to railroads willing to put up hotels. The idea was to draw visitors to the parks, drumming up public support that would allow them to expand.

This was good for the service, but not necessarily for the resources it was supposed to protect. In Yellowstone, for example, the Northern Pacific Railroad built a huge hotel on the shore of Lake Yellowstone, offering patrons spectacular views. But the hotel fell smack in the middle of the park's finest grizzly bear habitat, creating problems that persist to this day.

"We'd probably do it differently today," Barbee conceded. "The national parks were not conceived as great reservoirs of naturalness. Nobody had heard of the word, 'ecology.' The parks were basically set aside as natural curiosities."

While park service officials say there are no plans to expand the number of overnight accommodations or add any significant new facilities at Yellowstone, environmentalists charge that concessionaires already have exceeded their congressional mandate to provide only those services deemed "necessary and appropriate."

During the winter there are snowmobiles for rent, and in summertime the marina at Bridge Bay does a brisk business in outboard rentals and guided fishing tours. "This is starting to look like the North Shore of Lake Tahoe," groused Don Bachman of the Greater Yellowstone Coalition, an environmental group.

"We're not saying: Get rid of all the operations; but how appropriate is it to sell Christmas tree ornaments in the park?" asked Michael Scott of the Wilderness Society, which has advocated moving many commercial services to so-called "gateway" communities on park fringes.

While summer is by far the busiest season at Yellowstone, conservationists also fear the effects of rising winter use, when animals are most vulnerable to stress from human interference. One proposal involves a planned 350-mile snowmobile trail linking Lander, Wyo., and West Yellowstone, Mont.; the trail would traverse Yellowstone for 37 miles.

Heavily backed by the Wyoming congressional delegation, the project is considered key to state efforts to boost winter tourism in the area. But environmentalists say it is a mistake. "What we object to is the precedent set by the construction and maintenance of a facility not directly related to the use and enjoyment of Yellowstone National Park," said Scott.

Inevitably, commercial development has created problems for the wildlife the park is supposed to protect.

Earlier this summer, for example, park authorities were forced to take the unusual step of removing a female grizzly bear to an out-of-state research facility because they were concerned about the safety of guests at a Lake Yellowstone lodge. Although park rangers had repeatedly moved the bear to remote areas, they could not prevent her from returning each spring to fish for spawning trout in streams near the lodge.

Environmentalists had argued that the park should keep the lodge shuttered until the end of the seasonal trout run, but park authorities said that would be impractical. "It's a developed area that's been there a hundred years," said Barbee. "The removal of {one bear} was not going to lead to the demise of the Yellowstone ecosystem, so we took her out."

Similarly, park authorities in the 1970s agreed to remove stores and campgrounds from the area known as Fishing Bridge, which is heavily used by grizzlies, in order to compensate for the building of a new village elsewhere. But the Park Service backed down -- only part of the development was removed -- after bitter opposition from the Wyoming congressional delegation, the local tourist industry and motor home owners.

"Occasionally, six bears wander through that area," said Terry Povah, president of Hamilton Stores Inc., which operates stores in the park. "To me, to take out multimillion-dollar facilities in favor of six bears -- and I'm a bear lover -- does not make economic sense."

Park authorities assert that wildlife populations are healthy -- federal officials are even considering a proposal to remove the grizzly bear from the list of threatened species -- and suggest that critics would do better to focus their attention on development threats near park borders, such as logging and mining, rather than fighting over park concessions.

"Okay, so people like ice cream. What does that have to do with anything?" asked Barbee. "That gets into a very squishy area of prescribing values. We've got so many battles to fight, as long as things are not totally outrageous, that's not an issue I want to get overly involved with."