Six thousand campers began trekking out of California's magnificent Yosemite National Park yesterday afternoon on orders from rangers trying to comply with the federal government shutdown that began Saturday. Another 950 campsites were emptied at Tennessee's Great Smoky Mountains National Park.

But at Mammoth Cave National Park in Kentucky, visitors who had their tents pitched by Friday night were staying: They were part of several exceptions to what was supposed to be the orderly shutdown of the government.

The shutdown, triggered by the inability of Congress and the administration to reach a compromise on the national budget, is really an evolving beast with lots of bureaucratic wiggle room, as evidenced by the differing plights of the campers.

"There's some discretion," said National Park Service spokesman George Berklacy. "On the first day I got the impression supervisors were locking things up and not pushing people out. There's probably a lot of wishful thinking going on."

The Park Service is one of the few federal agencies that has employees working over the three-day Columbus Day weekend. A force of about 1,000 rangers -- out of a total of 12,000 -- was on the job yesterday at the agency's 356 park sites, Berklacy said.

Those who worked did so because they were needed to shut operations down or were deemed "essential," a designation left to each department to decide according to its count of people needed to protect public health and safety.

As at federal agencies that might face the 'Who is essential?' question Tuesday without approval of another stopgap funding measure and a budget resolution, "essential" is in the eye of the beholder.

During the one-day government shutdown Nov. 23, 1981, the Defense Department declared all its employees essential while the Education Department sent just about everyone home. The Agriculture Department laid off half its staff, while at Justice no one left. In fact, only about 250,000 of the government's 2 million employees left work and another 300,000 "nonessential" employees stayed on the job to shut down their agencies.

President Bush has said Federal Aviation Administration air traffic controllers are exempt from the shutdown, as are most prison guards, U.S. marshals, weather forecasters and FBI, Drug Enforcement Administration and Customs agents. Meat inspectors are essential and so are all medical personnel in the Veterans Affairs Department's 172 hospitals. The self-supporting U.S. Postal Service is unaffected.

Previous presidents have claimed "inherent power" to keep vital government functions operating during similar lapses in federal appropriations. President Jimmy Carter's attorney general, Benjamin R. Civiletti, concluded just before Carter left office in 1981 that the president had "inherent power" to protect public health and safety, regardless of legislation prohibiting the executive branch from spending what Congress has not appropriated.

In a Nov. 17, 1981, memorandum to the heads of executive departments and agencies, David A. Stockman, President Ronald Reagan's director of the Office of Management and Budget, elaborated:

"This memorandum is principally directed towards the ability of agencies to obligate funds in the absence of appropriations. It should be made clear {to employees} that, during a {sic} appropriations hiatus, funds may not be available to permit agency payment of obligations. All personnel. . . should be assured that the United States will not contest its legal obligation to make payment for such services, even in the absence of appropriations."

Employees were paid retroactively in the three government shutdowns of the 1980s.

OMB has instructed all federal employees to go to work Tuesday. If there is still a budget impasse, they are expected to shut down operations and be sent home within the first three hours of the day.

At Yosemite, 30 employees stayed on to help close the campgrounds, including several law enforcement rangers and maintenance workers. At Mammoth Cave, five rangers were left, along with one maintenance supervisor, who is "essential" because he has to check the chlorine level in the park's sewer systems.

Not many on the president's staff were deemed essential: 65 of the 383 White House employees, including all assistants to the president, all his legislative staff and staff members of the National Security Council, a spokesman said.

Ten employees attended to the needs of the president and the First Lady at the White House residence. There is only one chef per shift, only one engineer and only one maid, the spokesman said.

The Capitol remained open yesterday and many tourists showed up in a spirited mood. When the House recessed at 4 p.m., a chorus of boos filled the House visitors' gallery.

The Washington Monument, the Smithsonian's 13 museums, the animal houses at the National Zoo and many smaller federally run park facilities have been closed since Saturday. The parks are open, but their campgrounds, visitor centers, collection centers, restrooms and other federal employee-staffed operations have shut down.

"Visitors with broken-down Buicks and bursted bladders were not happy campers," Berklacy said.

Michael Joyce, a chiropractor from Chico, Calif., and his six friends were some of the unhappy campers made to leave Yosemite yesterday. "It's weird how we were affected so directly by something so far away," he said.

Callers to the White House comments line, which lets the public record messages for the president, also were disappointed. A recording gives out this message:

"We regret we're unable to say when the comment lines will reopen due to Congress's failure to pass the budget resolution." Click.