THE idea of national parks is one of America's best. Approval ratings exceed 90 percent. But political federal management of the parks is a terrible idea. Politics promotes ecological destruction and ethical corruption

Two recent books, "Playing God in Yellowstone" and "Rocky Times in Rocky Mountain National Park," publicize what experts have known for years: our parks' long-term ecological health is seriously threatened.

One problem is severe elk overpopulation. Elk in Yellowstone and Rocky Mountain National Parks far exceed the number the parks can sustain. There are 40,000-50,000 elk in the Yellowstone area, though it is the 20,000 elk inhabiting the northern range and wintering in the park that are the main problem. The burgeoning elk population is rapidly destroying aspen, cottonwood and willow stands and various grasses. Erosion is increasing and vegetative diversity is falling. Antelope, bighorn sheep, moose, mountain lions, ptarmigans, and beaver are among the victims.

Why does the Park Service permit elk to degrade the land and ecology in Yellowstone and Rocky Mountain? The answer is politics. Until 1967 (1961 in Rocky Mountain), the Park Service culled herds with government hunters. With natural predators and hunting by native Americans virtually eliminated, historic range severely reduced, and relocation no longer an option, slaughtering elk was the only responsible action.

But the public sees elk as cute and fuzzy charismatic megafauna that shouldn't be shot. Because the Park Service and its congressional overseers are sensitive to voter pressure, the elk population is exploding even as ecology, land quality and species diversity degrade.

Absence of fire is the second problem. Both Yellowstone and Rocky Mountain are fire-driven ecosystems. Fire is crucial for rejuvenating stagnant climax forests because it stimulates the growth of diverse succession species such as aspen and various grasses, shrubs and wildflowers. Lack of fire, particularly in Rocky Mountain, is destroying these species and the animals that depend on them. Before white men imposed a fire-control regime, low-level surface fires cleared away accumulated undergrowth while leaving most mature and healthy trees alive.

Ecological vitality is fostered by regular, small-scale burns. But once again, political pressure has made such burns difficult to tolerate, let alone create. Residents of nearby towns dislike smoke and haze from fires. Even controlled fire annoys tourists. And fires may escalate out of control.

Ultimately, as fuel accumulates, large fires are inevitable. Without the natural firebreaks created by less severe, more frequent burns and with the huge buildup in deadwood and other fuel (up to 100 tons/acre), a dry year may bring another fire such as that which burned 1.2 million acres of Yellowstone in 1988.

Perversely, fires actually help the Park Service. The Park Service is rewarded for uncontrolled fires because Congress grants blank checks for fire fighting. Besides, fighting fires is macho and romantic. As a smoke jumper friend said: "Fires are great! It's just like war but no one shoots back!"

Dr. Fred Wagner, director of the Ecology Center at Utah State University, notes another reason why destructive elk- and fire-management policies have continued: The people best qualified to criticize have been co-opted by the Park Service. Park Service scientists are well aware of an important ecological principle: Don't bite the hand that feeds you. In a 1989 paper, Wagner notes a recurring theme among researchers working with the parks. They say "Yes, I have some misgivings about what is going on in the parks, but I'm getting research funds from them and I'm not going to rock the boat." The consequence of this self-censorship is poorly informed policy.

To end the ecological damage of political management, we should consider alternative arrangements for park management. Public but nongovernment endowment boards operating under the common law doctrine of "trust" hold great promise. Everyone is familiar with institutions managed by endowment boards: nongovernment schools, nonprofit hospitals and museums are common examples.

Each park would have an endowment board. It could be chartered with the legally binding mandate of fostering the values that justified creating that park, e.g. wilderness, waterfowl or wonders. Established environmental groups, local communities and business leaders would nominate people to the board. Each person would be confirmed by Congress, and each park given a modest, one-time-only financial endowment. Free from political interference, the trustees would have responsibility for managing that park in accord with its charter.

An endowment board would solicit donations and charge fees just as a museum does. The board would have strong incentives to allow ecologically sensitive commercial activities, as we find on Audubon Society preserves and Nature Conservancy land. In rare cases, some extractive activities would be permitted, but only if they complement our national parks' highest values of scenery, preservation and recreation.

Freeing the parks from politics is essential to preserving their ecological and cultural legacy. We've had more than 600 years of experience with trusts. By making park managers accountable to a stable board of trustees rather than elected politicians with transient interests, they would be forced to confront the real, long-term consequences of their actions. Freed from the pressures of special interests, humans and nature could seek responsible balance.