At the Bighorn Canyon National Recreation Area, a floating comfort station is being repaired. At the Everglades National Park, rotting wooden planks on elevated trails are being replaced. In Alaska, meanwhile, an emergency radio communications system is being installed in the Gates of the Arctic National Park and Preserve.

The projects are among hundreds that the Interior Department has undertaken over the past four years as part of its Park Restoration and Improvement Program (PRIP). Now the administration says it has cleared up the backlog of health and safety problems that it found when it took office and wants to end its five-year effort a year ahead of time.

Since 1981, the department has spent nearly $1 billion on projects designed -- in the words of one Park Service official -- to give park visitors a memory more pleasant than an attack of "Montezuma's Revenge."

By the end of this fiscal year, the department will have spent $431 million on capital improvements (mainly water and sewer systems), $275 million on park roads, $115.2 million on other health and safety improvements and $97 million for historic rehabilitation.

According to C. Bruce Scheaffer, the Park Service's budget chief, spending on park repairs and improvements grew from $78 million in fiscal 1981 to an average of $250 million over the next four years. Now the administration wants to cut that to $106.3 million in fiscal 1986, and some congressional observers are concerned about letting the maintenance problems pile up again.

"They say that they're going back to the 1981 funding levels," said an aide to Rep. Sidney R. Yates (D-Ill.), chairman of the House Appropriations subcommittee on the interior. "But if the 1981 levels produced the problems that caused the administration to establish the PRIP program, what is that going to solve?"

Paul C. Pritchard, president of the National Parks and Conservation Association, testified before Yates' subcommittee that "one of the most obvious needs facing the system is consistent funding . . . not unwarranted reductions."

Clay Peters, a national parks analyst with the Wilderness Society, said the "program was appropriate, but it was a terribly misplaced priority."

From Peters' point of view, money should not be directed at correcting health and safety threats while funds are stripped from programs designed to acquire new parkland. "The administration married the two," he said. "That was wrong."

The program was developed after the late representative Phillip Burton (D-Calif.), then chairman of the House Interior subcommittee on national parks and insular affairs, pressed the Park Service in 1980 to prepare a comprehensive report on the state of the parks.

The study detailed thousands of problems, providing the basis for a program that Park Service Director Russell E. Dickenson developed and presented to then-secretary James G. Watt after he took office in 1981.

"Initially Watt reacted with a degree of skepticism," Dickenson said. "What I explained to him was that we needed a shift in emphasis from the continued growth of the national park system to a maintenance program." After Watt reviewed the five-year, $500 million program, he decided to propose doubling the request for funds..

But Pritchard said the lesson the administration learned is being lost through its seeming desire to revert to a "feast-or-famine cycle. The critical need is for consistent support for what is called 'planned deterioration' of significant structures." He said "what we don't want is for the parks to be flooded with a carbohydrate-sugar high and then put on a crash diet."

Hooper Brooks, director of a citizens' committee that advises the Gateway National Recreation Area in the New York City area, said the effort has not solved all the problems and has virtually ignored the needs of urban parks.

"The East has fared much more poorly than the West," he said. He cited a bathhouse on Staten Island that is threatened by an eroding shoreline. "It's hanging out over 30 feet of air because the seawall has washed away underneath . . . . Figuratively and literally, parts of Gateway sit there and continue to rot."

But Interior's Scheaffer said that future funding will take into account all safety problems -- even those in urban areas. "We're not going to neglect any of our visitors," he said. "We never can do everything . . . but you don't have to have a backlog of projects. We are now caught up for the first time in decades."