Perils of a Popular Park. Tourists, cruise ships, and land developments pressure small Caribbean preserve. VIRGIN ISLANDS PARADISE

HERE on the island of St. John, smallest of the United States Virgin Islands, there's one taxi for every 50 permanent residents. So brisk and booming is tourism that it's said most of the 100 native taxi owner-operators earn more than the superintendent of the region's main attraction, Virgin Islands National Park.

Salary aside, the park superintendent's job is not one to be relished except by those who love challenges.

He must work with a local population inherently mistrustful of the park, with pressures of land development within park boundaries, with wild donkeys that chase tourists and mongooses that threaten the sea turtle population, and with cruise ships that funnel more than a million visitors annually into the second-smallest and possibly the most fragile of all the national parks.

What's happening here?

To some extent, at least, part of the cloud that dims the park's future began gathering at its very founding.

Virgin Islands National Park owes its existence to the philanthropy of Laurance Rockefeller, who purchased and gave to the United States 5,000 acres of land on the island of St. John in the 1950s. That formed the core of the national park established in 1956 and enlarged to 6,955 surface acres since then.

But Mr. Rockefeller was unable to acquire consolidated blocks of property. The park is fragmented by 261 separate tracts of private land totaling 1,600 acres, some so valuable that the cost of a single building site may exceed Rockefeller's total investment.

Three years ago, one Virginia developer paid $6.8 million for a 35-acre hillside plot surrounded by the park. The developer then offered to sell it to the government for his purchase price, minus three choice building sites he and his partners would retain for themselves. The offer fell through when Congress failed to appropriate the necessary funds. The owners began subdividing and building roads.

Twenty lots from a half acre to two acres in size are now for sale at prices from $500,000 to $1.2 million. One new luxury residence is under construction, and others are sure to follow as the park, helpless to act, is made witness to its first subdivision.

Development virtually anywhere on the island presents problems.

Much of St. John is mountainous, with slopes up to 50 percent. When building sites are cleared and roads built, erosion follows, and there are scarred shoreline areas where soils washed from the hillsides have buried coral formations that constitute some of the national park's most fragile attractions.

The coral gardens have even worse tormentors, however, in the charter boats and cruise ships that anchor in the quiet bays of St. John every day and night (see sidebar).

The cruise ships and their seemingly endless cargoes of sun-seeking passengers are seen by some as the heart of the national park's problem. At midweek, as many as 12 big cruise ships arrive daily in Charlotte Amalie, the port on the neighboring island of St. Thomas. Some ships weigh as much as 75,000 tons and carry as many as 2,600 passengers. Last year cruise ships alone deposited more than a million visitors here.

Upon disembarking, most passengers head by ferry to St. John and the national park that occupies about 54 percent of the island's surface area. (The park also claims 5,649 acres offshore, to encompass the best of the coral gardens.)

If the cruise lines, the merchants, and the taxi operators are the beneficiaries of this ever-growing trade, however, the national park is viewed by many as a victim.

``These people [cruise ship operators] can't keep coming in here and using the park without helping to pay for it,'' says Ron deLugo, the Virgin Islands' lone elected delegate to Congress. He says the 25 or so cruise ships that regularly visit the islands contribute nothing directly to the park's welfare.

Michael Frome, a conservation writer who has visited the park for 20 years, said last winter: ``We must put a limit on the cruise ships. It's a small, fragile park, and it can't accept the dumping of cruise ship passengers for an afternoon joy ride.''

Park facilities designed and built 20 years ago for far smaller numbers of people are showing signs of collapse. At the height of winter tourist season, park rangers say, you can locate the restrooms at popular Trunk Bay Beach either by the odor or by long lines of waiting visitors. As often as not, the restrooms are inoperative for up to a week at a time because of burned-out pumps and overloaded septic systems.

``It's not the way we like to treat our visitors, and it's hardly up to the standard the National Park Service seeks to maintain,'' says Richard H. Maeder, the park's immediate past superintendent.

The tall, slender Kansan retired in early March after two years as chief of the Caribbean park. It was, he said, by far the most difficult and demanding role of his 34-year park career.

Today, because of budget cuts and other factors, increasing numbers of visitors are less and less likely to even see a park ranger. The park is compelled to operate with 12 positions vacant in order to accommodate a $284,000 budget shortfall. Transfers and recent retirements account for six additional positions, leaving the park 18 positions below full complement. That's 31 percent under strength.

The park's maintenance division chief, Richard Schneider, says conditions here are reminiscent of those during his Peace Corps experience in the Philippines.

``People back home are always envious when they hear I work at Virgin Islands National Park,'' he says. ``I tell them it's a great place to vacation, but a difficult place to work.''

Mr. Schneider's division is responsible for maintaining 21 miles of trails and 18 miles of roads. Yet the ``crew'' assigned these tasks consists of one man equipped with a tractor, flail mower, and backhoe.

The division is also responsible for 256 historic structures in the park, most of them the remains of old Danish sugar mills and plantations. But funding will allow stabilization work on only six. The rest are slowly turning to ruin under the effects of tropical rains and jungle-like vegetation.

For others on the park staff, the concerns are mongooses and donkeys.

Danish planters imported the mongoose in the 1700s to combat rats that infested the sugar cane fields. They flourished, had little if any impact on the rats, and today number in the hundreds, possibly the thousands. Among their favored foods are the eggs of the green and hawksbill turtles, both endangered species.

Donkeys are descendants of those used for transportation by island residents up until the time that roads and vehicles were introduced to St. John around 1950. No longer needing the animals, natives simply turned them loose to fend for themselves. Now their numbers have increased to more than 300, and they thresh about in the undergrowth and long roads and beach areas, mooching foodstuffs from visitors and occasionally invading tents and trash bins.

When several of the animals began chasing and nipping visitors, park rangers shot 10 of the worst offenders last fall. That triggered a wave of protests, particularly among natives who see the donkeys as symbols of their culture and heritage.

The park and island officials are weighing a number of options, among them a plea for residents to ``adopt'' some of the animals.

Despite their stirring defense of the animals, no residents have yet stepped forward to claim one.