Western US wilderness under siege. Lake Powell: will the `jewel of the Colorado' become `Beer Can Hill'? Tourists, lured by 1,960 miles of shoreline, may be ruining a pristine lake

Tour boat pilots like to take their Lake Powell visitors into silent canyons that mirror 700-foot-high sandstone cliffs and there proclaim that the water is so pure you can drink it without concern. Hidden away in sunny alcoves, they say, are archaeological sites that have escaped human trespass for 1,000 years.

Yet here in the Glen Canyon National Recreation Area along the Arizona-Utah border, National Park Service rangers will point out a site they call ``Beer Can Hill'' and offer accounts of remote beaches befouled by litter.

This is part of the price that Glen Canyon and Lake Powell, which is promoted as the ``jewel of the Colorado,'' appear to be paying on the way to becoming the fastest-growing recreation site in the Western United States.

Lured principally by the blue-water lake that extends a distance equivalent to that between New York and Baltimore, 2.8 million visitors came here last year to explore many of the Powell's 96 major canyons and 1,960 miles of shoreline. At times they produced mile-long lines of traffic at the more popular boat-launching sites. In canyons popular for overnight use, campers have been known to discharge firearms to drive off too-close neighbors.

Responding to public demand for services, Lake Powell and Glen Canyon are embarked on the biggest building and development program of any area in the 335-unit National Park System. Included in this effort are two new marinas (to join the six already existing), lodging, restaurants, employee housing, a fast-food complex, launching and boat-storage facilities - even a new airstrip.

Everyone, it seems, wants a piece of the action at this booming resort area. The principal concessionaire, Del E. Webb Recreational Properties, recently announced its intent to sell its five marinas and fleet of more than 300 rental houseboats as part of a corporate restructuring.

The Navajo Indian Nation, whose reservation extends for more than 200 miles along the southerly Lake Powell shoreline, operates a small interim marina along the San Juan River arm of the lake. Soon, the Navajos will have another major marina at a site adjacent to the town of Page, Ariz. (pop., 6,500).

San Juan County, Utah, is sponsoring the construction of a new airstrip to accommodate fly-in visitors to the up-lake marina at Hall's Crossing. It would replace a dirt airstrip that offers unsafe approaches over Lake Powell.

Utah officials complain that, while 95 percent of Lake Powell is within that state's boundaries, Arizona, which has the largest marina on the lake, gets most of the money spent by visitors. ``Our shorelines may be impacted and polluted, but the revenue goes to Arizona,'' fumes Cary Peterson, majority leader of the Utah Senate.

Others dispute this claim.

Seeking to correct this professed imbalance, Utah Gov. Norman Bangerter offered to exchange scattered state lands with the federal government last year for 60,000 acres of Lake Powell shoreline where, he said, the State of Utah would construct five marinas. Washington declined the invitation.

As a summer escape for city dwellers, the 1.2 million-acre area has, in 16 years, become something of a prodigal goose laying golden eggs.

``But whose goose is it?'' asks Terri Martin of the National Parks and Conservation Association, which questions how much development the area can absorb. ``I've heard some awful complaints about the place - that you can't find a good shoreline campsite, that you can't go up a canyon and not find a houseboat traffic jam. There ought to be a study to define limits of acceptable change, and proceed from there.''

Perhaps nowhere more than here does the Park Service face greater challenges in attempting to ensure adequate protection of a park's resources while at the same time accommodating the demands of its visitors.

``The National Park Service perception of what people should have is strongly colored by what those people demand,'' says Ron Everhart, a career ranger who oversees the operations of Glen Canyon's principal concessionaire. ``We get to be the final arbiter, and it's not an easy or comfortable role.''

When Lake Powell first began filling in 1963 behind the closed gates of massive Glen Canyon Dam, planners forecast that the recreation area might have half a million visitors by the year 2000. Yet by 1986 the are recorded 2.5 million visitors, five times more.

Problems are as acute in the remote canyons as in the marinas, where there are no facilities. Shore-camping visitors are fouling beaches, even though regula-tions prohibit the disposal of waste within 100 feet of a water source. Some have intruded on known archaeological sites and defaced delicate panels of prehistoric Indian art with bullets and graffiti.

``The fact is that we have the equivalent of only 128 employees - rangers, interpreters, maintenance workers, and administrative people - spread over an area of more than 1 million acres, with the second-largest man-made lake in the nation, and with nearly 3 million visitors,'' says Glen Canyon's superintendent, John Lancaster.

``It is trite to say, but we simply need more money and more people to adequately protect and manage the area.''

Part of that money and additional staff, Mr. Lancaster says, would be used to better direct visitors and influence their wider dispersal over this sprawling area. Also under study, Lancaster says, is a requirement that campers use portable toilets and adhere more rigidly to carrying out whatever they carried in.

Still, there remains the question of how to determine the acceptable level of use in a popular national park area.

``That's what our management plans are intended to address,'' says Lancaster. ``The problem is, the dynamics of visitor use sometimes run well ahead of our planning, our ability to buy what we require, and our ability to mitigate the damage.''

Terri Martin of the National Parks and Conservation Association shares his concern. ``You just can't expect one park to continue to absorb more and more growth,'' she says. ``If we're going to have that kind of growth, then let's have more parks.''