HIGH up the Cascade Mountains, Crater Lake National Park can be warm and mellow this time of year. The campgrounds are empty, the Winnebagos few and far between, the gift shop quiet. A few tourists peer down from the rim to the dark blue lake 1,000 feet below, created 7 millenia ago when Mt. Mazama blew its top with a force 42 times greater than Mt. St. Helens.The fall calm is deceptive, however; during the summer Crater Lake - like many national parks - is wall-to-wall people, its campgrounds packed, its rangers turned into traffic cops. "My people are strapped," says chief ranger George Buckingham, a 27-year park service veteran. "They're having to decide what to do ... and it's hard for a ranger to have to choose between protecting a resource and serving the public." The National Park Service celebrated its 75th anniversary recently facing serious questions about its purpose and its future. Among the major problems: overcrowding, limited management and maintenance resources, encroaching development, and a system of private concessions that critics say is monopolistic and far too profitable. Meeting in Vail, Colo., earlier this month, several hundred Park Service professionals, environmentalists, educators, and politicians talked through these problems and heard senior government officials pledge a new era of protection for the parks. "Clearly, our overriding responsibility is the stewardship of natural, cultural, and recreational resources both in the parks and throughout the country," declared Park Service director James Ridenour. "To fulfill this role, we have to move ourselves back to the frontier of good science and good research." United States Secretary of the Interior Manuel Lujan told the group "the mission of the Park Service is, first to protect the resource and, secondly, to provide enjoyment by the public." "But when push comes to shove, " he emphasized, "we've got to protect the resource." As experts realize that a park's ecosystem extends beyond politically-determined boundaries, this will put park protection at odds with such activities as mining, logging, and ranching. This is especially true around Yellowstone, where the Park Service's Rocky Mountain regional director recently was transferred back East for pushing too hard for environmental protection. In some cases, it may involve conflicting interests between federal agencies. In his office at Crater Lake, Mr. Buckingham kneels on the floor to spread out satellite photos taken by infrared camera. The park is surrounded by National Forest land, and the photos show clear-cut logging has occurred all along the border. "The pressures are getting worse, and what scares me the most is that we're running out of room. Civilization is pushing up against the parks," he says. Park Service data gathered by the Wilderness Society shows that ozone levels due to air pollution at about six parks routinely are above the point set by the Environmental Protection Agency as unhealthy. With more than 250 million visitors a year, the environmental group reports, "steadily growing automobile traffic is bringing 'greenlock' to more and more parks." Parks director Ridenour's call for more scientific research to protect natural resources will necessitate either a bigger budget or shifting funds. At present the Park Service designates just 3 percent of its budget for such research. Crater Lake has two biologists to oversee nearly 200,000 acres of forest and aquatic habitat, and ranger Buckingham says he "could easily use four, five, or six." Economic development within the parks is seen as a major concern as well. This includes about 560 concessions - from snack bars to luxury hotels and marinas - in 126 National Park units. Under current law, concessionaires operate on long-term contracts ranging up to 30 years and receive preferential treatment when it comes time to renew. The US General Accounting Office reported this summer that the average return to the federal government is only about 2 percent of gross revenues. Paul Pritchard, president of the National Parks and Conservation Association, says this amounts to a system of "licensed monopolies." Legislation proposed by Sen. Dale Bumpers (D) of Arkansas and Rep. Mike Synar (D) of Oklahoma would increase competition for contracts, shorten contract time, and encourage higher franchise fees. Beyond that, there is growing pressure to scale back the extent to which the comforts of civilization have become part of the "park experience." "The time has come to decide that the national parks will be a breed apart from amusement parks," states a report by the Wilderness Society setting 10 goals for the park system. "Commercialism must be scaled back." Meanwhile, routine work at the parks is stacking up - $2 billion in backlogged maintenance, according to Mr. Pritchard. "At Yellowstone National Park, 60 percent of the roads are in dire need of repair, and that goes for the trails also," he said in releasing his organization's report timed to coincide with the park service's 75th anniversary. "The national park ranger is becoming an endangered species," Pritchard warns. "A decade of budget cuts has resulted in hundreds of ranger positions going unfilled, creating serious problems within the resource management, personnel management, and visitor safety programs," he said. "The ratio of rangers to visitors is at an all-time low." There are also concerns about the quality of training for rangers and other Park Service employees. At the Colorado meeting, Ridenour conceded that "the tradition of professionalism ... could not be more at risk." Under the Bush administration, the Park Service budget has edged up to about $1.3 billion a year. There have been efforts to reduce power plant emissions near the Grand Canyon and create buffer zones to protect the Florida Everglades. Still, a group of eight experts recently gave the White House a grade of "D-plus" for its stewardship of the parks.