Aerial crusaders. One picture is worth a thousand-page environmental impact statement; so a group of volunteer pilots is helping to shape public opinion by showing legislators startling bird's-eye views of pollution damage

The inland flight to Olympic National Forest is as majestic as any in America: Snowcapped mountains pierce a 3,000-foot ceiling of marshmallow cumulus that sandwiches our tiny, Cessna 185 between mist and towering spruce. Our hawk-sized shadow glides over glistening wavelets of Puget Sound, over houses the size of Monopoly hotels with woodpiles that look like stacks of toothpicks. ``Let's take a look up above,'' says my pilot, Michael Stewartt, as we swoop up into the cloud ceiling and over the first peak, about 45 minutes inland. ``There you go,'' he says, ``this is what flight can show you - people don't know this is going on.''

Spread before us is a 20-square-mile stretch of peaks and valleys that look like a marine haircut gone awry: entire mountainsides shaved down to stubble or bare dirt, leaving only the indent of logging roads spiraling to the top like the threads of a corkscrew. For the next hour we will navigate hundreds of feet above the ground, wielding a Nikon out the small, hinged window for aerial documentation.

This day's flight with a single journalist - later with a group of environmental experts - is a way to trumpet the plight of the shrinking primeval forests of the Pacific Northwest, and the further threat to an entire disappearing ecosystem. Lighthawk pilots are aerial crusaders in the cause of conservation. This year they will fly similar missions from Alaska to Costa Rica, logging about 150,000 miles, spotlighting environmental hazards from waste dumps to spewing smokestacks, strip miners to illegal squatters.

The Santa Fe-based group of pilots and volunteers named themselves after a mythical bird ``whose purpose is to shed light,'' says Mr. Stewartt.

The key point Lighthawk wants to make is visceral and visual; something beyond statistics and environmental reports. By showing citizens, journalists, and legislators the impact of, for example, a proposed nuclear waste site just one mile from Canyonlands National Park in southeastern Utah, Lighthawk can help shape public opinion on environmental controversies.

Formed about 10 years ago, and now with hundreds of projects under its belt, Lighthawk is working with the Seattle Wilderness Society to chronicle the number of acres of old forest growth left. The figures will be compared with those of the United States Forest Service. Discrepancies - early estimates differ by hundreds of thousands of acres, says Stewartt - will be shared with journalists and legislators, in an effort to reverse the logging trend.

``Lighthawk is one of the most important and effective conservation efforts in the US today,'' says George Frampton, president of the Wilderness Society, one of more than 100 conservation organizations that have employed Lighthawk's services. ``If we (environmentalists) are going to build a public constituency and educate them about the importance of protecting these lands, then we are going to have to inspire them. Project Lighthawk inspires people in a very direct and effective way.''

It was an aerial mission such as this in the mid-1970s that led Stewartt to found Lighthawk, not only to spotlight environmental problems but to help solve them. (Pilots and planes are also used for such purposes as a recent airlift of an endangered grouse, which may have become extinct had Lighthawk not rallied in very short time to save the world's last 14 birds.)

In 1974, Stewartt had been a pilot for commuter airlines in Colorado and the Caribbean, as well as bush pilot in Nome, Alaska. A native of Tucson, Ariz., he offered to assist a Santa Fe environmental group opposed to the construction of a massive coal-fired power plant on the Kaiparowits Plateau in southern Utah. When a press conference was organized to spread the word that pollution from the plant would spoil views of the nearby Grand Canyon and other parks, Stewartt organized planes and pilots to help photojournalists and network camera crews take a look.

The resulting news media coverage caused such public uproar that officials of the proposed plant scrapped the project. Many lauded the individual initiative of Stewartt. Four years later, in 1978, with a single plane, Lighthawk was off the ground. Today, two planes, two staff pilots, and seven volunteer pilots log hundreds of thousands of miles a year.

The result has been a string of victories for environmentalists. Among them was the closing last year of the Phelps Dodge copper smelting plant in Douglas, Ariz., which was for 40 years the largest single source of sulfur-dioxide emissions - a major component of acid rain - in the US. Lighthawk helped bring about national media exposure, flying journalists, politicians, and experts over the remote plant site, near the Mexican border, where no commercial airlines flew.

On their own initiative, Lighthawk members helped expose illegal logging and gold mining in protected land called the Osa Peninsula, adjacent to the Corcovado National Forest in Costa Rica. Pilots photographed clearcut forests and burned pastures at low altitude and presented them to the minister of natural resources, Alvaro Humana Quesada. Later trips revealed stripping of stream beds, expressly forbidden in contracts with gold miners.

And in the Tongass National Forest of Alaska, Lighthawk has for more than a year been showing congressional and conservation leaders the results of the federal government's logging subsidies. In 1986, for instance, the US Forest Service spent more than $53 million to build logging roads and promote commercial timbering there. In return, it received $86,000 in total revenue from the sales of the trees. ``Trees that are over nine feet in diameter and 100 feet tall are sold for $3 each and turned into pulp for Japan's chemical and paper companies,'' says Lighthawk's Steele Wotkyns.

Besides seizing upon headline-grabbing issues, Lighthawk has developed a history of making airplanes available on the cheap (at about cost: $35 an hour) to smaller organizations.

``Lighthawk has really given the conservation community in the West some wings,'' says Darrell Knuffke, Central Rockies regional director of the Wilderness Society. Mr. Knuffke says he has used Lighthawk services 15 times in the last two years. One of the latest was to fly a top aide for Rep. Silvio Conte (R) of Massachusetts, a ranking minority member of the House Appropriations Committee, over private land blocking access to the Colorado National Monument.

``There are lots of flying services, but Lighthawk does it for some fraction of what commercial services would charge, and they will do whatever it takes,'' says Knuffke. ``Even if they have to set us down on a little dirt strip in the Utah desert.''

``They are always there to accommodate themselves to the needs and schedules of people who are looking at tough environmental issues,'' says Jim Cubie, a senior counsel on the staff of Sen. Patrick Leahy (D) of Vermont. As counsel to the Senate Agriculture Committee that has authority over the national forest system, Mr. Cubie has been examining conflicts among developers, miners, and environmental groups.

``Given the amount of time I had, there is no way I could see the area of southwest Colorado without Lighthawk,'' says Cubie.

Flying clients for cost means Lighthawk is always in the business of soliciting donations.

``We need money badly,'' says Stewartt, who is looking to add a helicopter, a land rover, and another plane that can land on water. Besides equipment, there are operating costs: $202,000 this year, nearly all from donations. As a nonprofit conservation organization, Lighthawk depends on foundation grants, individual donations, client fees 10 percent), and $35-a-year membership dues.

It was the donation of a Helio Courier bush airplane and 150 hours' worth of fuel that got Lighthawk's first clients up over a proposed dam site on Colorado's Gunnison River. Builders reconsidered plans after Lighthawk found that valuable archaeological digs would be flooded if the proposed site were used.

Two years later, donations of $60,000 enabled the purchase of Lighthawk's first turbocharged Cessna 210. Four years later, a second plane was added.

Besides expanding with bigger and better airplanes, Lighthawk is now initiating projects on its own without waiting for clients. Until now, 90 percent of its business was from groups such as the Nature Conservancy, the National Wildlife Federation, the Sierra Club, the National Geographic Society, and the Wilderness Society.

But two recent Costa Rican projects were Stewartt's initiatives. One, focusing on the Cathedral Rain Forest Science Preserve, received this fan letter:

``The donation of your impressive service has enabled us to proceed with the Costa Rican government in the identification of gold-mining and farming activities on the preserve, as well as in Costa Rica's Gulf Vulce Forest Preserve,'' writes Arnold Newman, vice-president of the International Society for the Preservation of the Tropical Rainforest. ``I want to add that in 25 years in tropical forest conservation, yours was the most spectacular flight I have experienced. I was amazed, in fact, to be able to find the very property in the enormity of the rough Osa terrain.''

``We're not just a bunch of pilots anymore,'' Adds Stewartt. ``We're following all the issues and asking what can we do. It's our connection to creative ideas about how flight can bring revelation about what's going on with an issue to bring it to its best possible resolution.''

In a July 14 article on pilots who help out in US conservation efforts, the caption under one of the photos was incorrect. It should have read, ``Washington's Olympic National Forest.''