From the Shenandoahs to the Cascades, US national parks have been pushed to the limit by their biggest summer ever. Some 84 million people tromped through a park this summer, according to National Park Service estimates. This represents a 17 percent increase over the previous year's number. A record 262 million visitors could breeze through the parks by the end of this year.
Indeed, many of the 334 federal parks are showing the wear and tear brought on by unprecedented popularity and a decade of tight budgets stretched to cover a vastly expanded system.
In addition, many of the most celebrated parks -- crown jewels of the federal system such as Yosemite and Glacier National Park -- are facing additional onslaughts by land development and urban encroachment.
``The parks are under serious threats, both internal and external,'' says Destry Jarvis, vice-president of the National Parks and Conservation Association, a Washington D.C.-based environmental group. ``Overcrowding is just one of the more obvious problems.''
High among the current concerns of observers in and out of the Park Service:
Air pollution in the national parks. Acid rain, thought to originate with burning of fossil fuels, is a serious problem in many parks throughout the East. Officials at Gettysburg National Military Park estimate it will cost $2 million to repair monuments there damaged by acid rain.
In the West, smog rolls periodically into parks such as the Grand Canyon and Yosemite.
Energy development around the parks. Near Wyoming's Yellowstone National Park, several proposals exist to tap the geothermal energy that powers scenic geysers like the famous ``Old Faithful.'' Opponents of the plans contend that the projects could divert much of the energy from park geysers, ultimately shutting them off.
Also, environmentalists and the Park Service are fighting a proposed hydroelectric development on the Merced River just downstream from the Yosemite National Park boundary. Opponents of the plan say the resulting dams and drainage facilities would result in the loss of winter habitat for Yosemite's deer, bear, and mountain lion population.
Environmentalists are also concerned about the attention rich fossil-fuel deposits in the western Overthrust Belt will draw if the world oil market should begin to tighten. Extensive tar-sand deposits lie in and around Utah's Canyonlands and Capitol Reef National Parks. Yellowstone and Glacier National Parks are also surrounded by rich mineral deposits.
Environmentalists say that a proposed open-pit coal mine in British Columbia, six miles from the border of Glacier National Park, threatens the park with air and water pollution.
The Park Service budget. Funds from the recent billion-dollar repair effort, initiated by former Interior Secretary James G. Watt, are running out. Many observers say that current park difficulties will be compounded if Congress approves the Reagan administration's plans to cut the Park Service's 1986 budget by 30 percent. For 1985, the Park Service budget is $908 million.
Yet Park Service Director William Mott insists that the cuts do not worry him and says the service can accomplish its mission with creative management. Mr. Mott has formulated a 12-point plan that is supposed to guide Park Service development over the coming years. As part of the plan, he is drafting proposals to add Grasslands and Wild River National Parks to the federal system, subject to congressional approval.
The plight of the parks, which include spots in such such far-flung places as the US Virgin Islands and Saipan, is also getting attention from a 15-member presidential commission. Among other subjects, the panel is expected to look into the possibility of raising visitor access fees as a way to control the number of visitors.