OUR NATIONAL PARK system is now engulfed by the gravest threats in its entire history of more than a century.

Pollution of air and water, commercial encroachment, overuse, improper assignment and lack of field personnel to protect the resources, are some of the critical problems that must be faced and solved in the 1980s -- that is, if our parks are to remain unspoiled, peaceful havens for travelers in search of inspiration and wholesome recreation.

The parks have proven their place in this country. From the establishment of Yellowstone in 1872 as the first national park in the world, this network has grown to embrace 330 units -- not only national parks, but archeological monuments, historic areas, national rivers, seashores, parkways and recreation areas. They are virtually everywhere in America, inexpensive and accessible, regardless of where one lives, and it is little wonder their popularity grows with the years.

New areas have been added to the National Park system, yet there is continuing need and demand to add more. That is understandable. These special places comprise a gallery of treasures that inspire, instruct and stimulate well-being. Our national parks, in fact, are an endowment of riches that make the United States the envy of the world.

Sen. Mark Hatfield (R-Ore.) recently commented that "Our national security has never been dependent on the amount of money we spend to protect ourselves; it is dependent on the value of what we protect." He might well have had the national parks in mind -- certainly the nation, and its people, would be poorer without them.

Yet the truth is that our "islands of hope" -- as these scenic, historic and cultural treasures have been called -- face all kinds of threats, pressures of commercialization and super-civilization that degrade and destroy their irreplaceable resources.

In the Southwest, for instance, some of America's clearest skies are likely to be turned into the dirtiest. Huge strip mines and coal-fired power plants, some already operating and others planned, are creating layers of smog over Grand Canyon, Mesa Verde, Zion, Bryce, Capitol Reef and Canyonlands National Parks, plus spectacular Monument Valley and the Hopi and Navajo Indian Reservations.

Toxic chemicals emitted from polluting industries are ruining air and water in these and other sanctuaries which Americans visit for relief from such poisons. The Clean Air Act makes specific provision for protection of national park and wilderness vistas, but the Act is up for reauthorization by Congress this year and industry is united in a lobbying campaign to weaken it.

"We should not think of turning the clock back," insists Paul Pritchard, executive director of the National Parks and Conservation Association, a leader in the National Clean Air Coalition. "The Act has improved air quality in most areas of the country and stimulated new technology in controlling pollution. It shows what can be done.

"Now we need to move ahead by regulating airborne toxic chemicals, curbing acid rain that endangers parks and other resources, and by clamping down on polluters who evade controls. Of course, regulations should be simple -- and they can be, as long as the goals are clearly defined and unmistakable."

There is plenty of pollution inside the parks. During years of growing popularity, Congress concentrated on making it easy for millions to enter the gates, but with scant attention to giving field personnel the means to supervise crowds or to protect natural values.

While in Yellowstone last summer, I never saw a ranger or sign of a ranger patrol during six days in the back country. The rangers are tied up coping with crowds around huge urban centers, like Canyon Village, built of concrete, asphalt and plastic, which have little if any relevancy to appreciation and enjoyment of a great natural area.

John Townsley, superintendent of Yellowstone National Park, told me of his concern about extensive game poaching in the back country: illegal shooting for trophy animals and for the antlers of elks which are shipped to the Orient, serving the same purpose (in concocting elixirs or aphrodisiacs) as the horn of the African rhino. But nobody knows the full scope of the damage because of the inadequacy of ranger patrols.

A steep price is being paid. Congestion, noise, intrusions of man-made structures, pollution from too many automobiles and vandalism all interfere with enjoyment of the natural scene, for which people flock to the parks in the first place. In a number of areas, standards of public health and sanitation are not being met.

he Colorado River, running through Grand Canyon National Park, is a case in point. The popularity of the river among travelers via rubber raft and boat has proven its own undoing, engendering problems of noise pollution, public safety, and destruction of natural and archeological values. In order to protect rivers for people, they need to be protected from them as well.

Last year the National Park Service reached a decision to phase out the use of motors on boats running the Colorado River. Though the ruling came only after several years of research and extensive public hearings, political pressure brought by commercial boatmen thus far has blocked implementation of the phase-out.

In western Wyoming, Grand Teton National Park is one of America's best-loved sanctuaries. Unfortunately, the pristine air and quiet of the park and the valley known as Jackson Hole are endangered by persistent pressures to accommodate scheduled commercial jets at what is the only airport located within a national park.

The airport actually was established 40 years ago, long before the site was incorporated into the park. Though it once might easily have been moved, many improvements have been made and there is pressure for still more. The Park Serivce has proposed a noise abatement plan, which the Jackson Hole Airport Board, local commercial and political interests have strongly opposed as an obstacle to boosting the tourist body count.

Critical problems occur not only in the natural areas of the West but at the historic and cultural monuments of the East. These are scarcely published or publicized, but a recent priority list of essential repairs prepared by the Mid-Atlantic Region of the Park Service shows these needs at Independence Hall National Historical Park:

Rehabilitation of the tower of Independence Hall; rehabilitation and updating of fire and intrusion alarms; correction of deterioration of various structural elements for seven historical buildings, and rehabilitation and correction of malfunctioning of climate controls.

And these needs at Fort McHenry National Monument: rehabilitate drainage system to reduce pressure on Star Fort walls, and install alarm system and fire suppression system.

Meantime, the National Park Service budget is being seriously reduced by the Reagan administration. A little austerity certainly induces better management, but the Park Service budget isn't much to begin with, a little more than $500 million.

Even James G. Watt, the controversial secretary of the interior, has stated that many of our finest parks have been chronically underfunded for years, that they need to be brought up to standards visitors have a right to expect. But this is not likely to happen soon.

Personnel are demoralized in the face of deep cuts. Various visitor services are being eliminated or reduced, but protection of resources will suffer more. As Russell Dickenson, director of the Park Service, concedes: "We must concentrate our activities where most of the people are."

The administration has been especially harsh in slashing the Land and Water Conservation Fund, the source of money for acquisition for land for federal parks, seashores, wild and scenic rivers, and of matching funds for comparable state programs. In terms of inflation and the nation's economy, these cuts are meaningless, since the Fund services its revenue from off-shore oil-drilling leases and can't be used for any other purpose.

Park supporters fear that delaying purchase of designated areas while prices escalate will only cost the public more and make land speculators rich. Sen. Alan Cranston (D-Calif.) recently accused the administration of undermining the new Santa Monica National Recreation Area by wiping out all funding for acquisition.

"The land is under extreme pressure by private developers and the value is rapidly accelerating," Sen. Cranston declared. "It must be acquired for the park now or an out-standingly beautiful coastal mountain region may be lost for public use forever."

While Secretary Watt has given personal endorsement to Director Dickenson (the only bureau chief at Interior to survive the ax) and has pledged to protect the parks, he has yet to demonstrate concern over threats to park ecosystems and wilderness. He could do worse than to take a clue from Walter J. Hickel, a former secretary of the interior under whom Watt served. In 1970, Hickel pleaded the need for setting aside more beaches, parks and recreational facilities in all sections of the country. mThen he added:

"At the same time, we need to protect more wilderness against the in-roads of injurious development and overuse -- not to keep people out, but to insure there will always be a lasting supply of wilderness for future generations to know and enjoy as part of their heritage."