THE HISTORY books tell us that the main legacy of Ulysses S. Grant's presidency was a sorry record of scandal and corruption. But the Grant administration also produced one of the most successful and influential governmental innovations in recent world history.

On March 1, 1872, Grant signed a law that may well have been the most original and influential in U.S. history -- a piece of legislation that historian Wallace Stegner called "the best idea we ever had."

This short page of legalese set aside "the tract of land . . . near the headwaters of the Yellowstone River" as a wholly new kind of official entity never before seen anywhere: the national park.

In an unprecedented feat of legislative grandeur, the Yellowstone Park Act designated a 2.2 million- acre rectangle -- an area larger than some whole states -- to be "a public park or pleasuring ground for the benefit and enjoyment of the people."

This bold new American concept spread rapidly across the globe, spawning 47 more national parks in the U.S. and some 2,600 others in 137 countries around the world.

But now a significant body of thought holds that Congress and Grant made a major -- and possibly fatal -- mistake when they set apart Yellowstone as the world's first national park.

These revisionists -- ranging from liberal environmentalists to Ronald Reagan's chief guru on park issues -- say that Congress' ambitious action was not nearly ambitious enough.

"Congress saved about 2 million acres, but the whole ecosystem, the biological and geological unit, extends more than 6 million acres," says Bob Anderson, director of the Greater Yellowstone Coalition, a union of 40 environmental groups.

"The problem is, since we didn't protect the whole ecosystem, we probably can't protect the wildlife and the geysers in the part of it that has been designated the national park."

Environmental groups have been working -- with singular lack of success -- for several years to win legal protection of the entire "Greater Yellowstone Ecosystem."

But this year the movement is getting a major boost.

In a monograph to be published later this year, Yellowstone Park Superintendent Robert D. Barbee argues that "Most of the . . . resource problems that Yellowstone National Park faces today trace back to its creation over 100 years ago."

Because of "the earlier Congressional oversight," Barbee writes, the Yellowstone area "has become an ecological island" with boundaries that "do not encompass a complete ecological unit, nor do they adequately protect the area's unique geothermal areas."

As head of the nation's flagship park, Barbee represents a key convert to the "greater ecosystem" idea. This month, though, the cause won an even more significant recruit i the person of William Penn Mott, Jr., the energetic park expert who ran the California state park system under Gov. Ronald Reagan and was just named by Reagan as the new chief of the National Park Service.

On a visit to Yellowstone, Mott endorsed the "greater ecosystem" idea and said he would work hard "to create a legal buffer zone around the park that represents the entire ecosystem."

An ecosystem, according to Webster's, is "a community of animals, plants and bacteria and its interrelated physical and chemical environment."

Because of encroachments of industrial man, many naturalists say there are only three complete ecosystems on earth that are still largely intact: the Arctic, the Antarctic and Greater Yellowstone.

One reason the Yellowstone region is still somewhat preserved is that the 6-million acre swath contains numerous federal reservations, including six national forests, several wilderness and wildlife refuges, and two national parks (Yellowstone and Grand Teton).

But there are significant dangers as well, because the Yellowstone region is greater than the sum of its parks.

This magnificent hunk of God's handiwork has always been home to a rich population of fish, fowl and land animals. Today, though, the ecosystem also contains an assortment of human creations ranging from Burger Kings and Best Westerns to jails, junk yards, oil wells, ski resorts, highways and hydroelectric dams.

The basic thesis of the "greater ecosystem" movement is that the environmental fallout from these human activities does not honor the neat bureaucratic boundary lines that Congress drew when it created the parks and preserves in the region.

Barbee, the Yellowstone Park superintendent, cites as an example the park's intensive effort to save the dwindling population of grizzly bears, the largest and best-known carnivore on the North American continent.

"In the park, we do everything we can to keep the grizzlies free of human contact so they can survive in their (natural) habitat," he says. "And then we find out that there's a bunch of them who go over to West Yellowstone (the Montana town five miles outside the park border) and have dinner in the garbage dump.

"When that happens, you've got a family of bears that may never go back to natural forage. Who knows if those bears can survive?"

Further, human development could endanger the unique geological features, such as the Old Faithful geyser basin, that prompted 19th- century visionaries to propose the idea of national park here in the first place.

In the towns to the west of Yellowstone, energy companies have proposed deep earth drilling to generate power from geothermal forces -- the intense heat that is fairly near the earth's surface in this geologically young region.

"There is mounting evidence that the aquifer feeding Yellowstone's geothermal features has its origins outside the park," Barbee writes in his new monograph.

"This, combined with the potential exploitation of the known geothermal resource areas adjacent to Yellowstone, shows why the recognition of this ecosystem is so important."

To date, the major achievement of the "greater ecosystem" movement has been to identify the general problem and point out some of the external threats to this world-famous natural preserve.

The Greater Yellowstone Coalition has put together a depressingly thick catalogue titled "Threats to Greater Yellowstone" which includes a "threat inventory" of nearly 100 human encroachments on the natural ecosystem.

But it is one thing to identify "threats" and something else altogether to do something about them.

The response in Congress to demands for legal protection of the entire ecosystem has been an indifferent shrug.

Rep. Dick Cheney (R-Wyo.), the influential Republican whose district includes most of the ecosystem, told a gathering of environmentalists on June 8 that the buffer zone plan "is not going to be an easy one to sell."

Ironically, the present patchwork of development was exactly what the first explorers of Yellowstone hoped to avoid when they came up with the startling suggestion that a "national park" be created to preserve this natural gem.

At a time when the government was eagerly selling or giving away its western lands -- and when powerful railroad interests were eagerly gobbling up any land of value -- the legislation setting aside Yellowstone as a public preserve was considered a daring political act.

The question now arises whether Congress can be as daring once again to save this marvelous park.