ACADEMY BAY, Santa Cruz Island, Galapagos - The Galapagos Islands is the sort of experience that gives you hope, on the one hand, that man-kind may yet learn to be part of the peaceable kingdom. There is unspeakable bliss in having wild sea lion pups jump fearlessly into your arms, of being just another creature sharing the planet with them and the birds instead of being the fear-bringing conqueror before whom all nature flees.

On the other hand, there seems to be no hope whatever that onrushing civilization with its plagues of plants, ants, goats, dogs and pigs (not to mention plastic) can be held totally at bay on the Galapagos, or, by extension, anywhere else.

The battle - and it is a battle - is fully joined here, where every import of godless civilization threatens the strange and wonderful balance that made the islands a famous laboratory of evolution.

"When you get right down to it, you either permit people to come and you try to control them, or you close the place down completely," said Craig MacFarland, director of the Charles Darwin Research Station. "Even so, the tourists aren't the biggest problem. It's the colonists who live here."

The scientists and the colonists have had an uneasy relationship ever since the Charles Darwin Foundation was established by UNESCO in 1959. Named after the famed biologist who based much of the theory of evolution on what he saw here, the foundation took on the task of promoting research while simultaneously helping - not to say prodding - the government of Ecuador to conserve and protect Galapagos wildlife.

Help was needed. Although farsighted conservation laws had been enacted in 1934, they had never been enforced. Grasses introduced to feed imported cattle fed nothing else in the island's unique ecosystem and spread off the ranches, pushing out native varieties. Goats brought in to provide meat ate the existing vegetation that supported the famous huge tortoises, for which the archipelago was named.

Packs of dogs gone wild killed the small dragonlike iguanas, while pigs and rats dug up the reptiles' eggs and ate their young. With no natural enemies here, the newcomers flourished.

"Three goats were put out on Pinta (an outlying island) in 1957; the National Park Service has shot 40,000 there since 1971," Dr. Fritz Trillmich informed a group of tourists visiting the Darwin Station recently. We sat panting from the equatorial heat in the shelter of the station's tortoise nursery building, donated by the San Diego Zoological Society.

Here tortoise eggs are hatched and the babies raised until they are big enough to fend off the rats. On the pillars of the airy building, another imported plague: red fire ants.

The tiny invaders, different from the U.S. version, are everywhere on the four inhabited islands, exploding in population and gradually eating their way through all the native ants. They live everywhere, eat anything and have no local natural enemies. They live everywhere, eat anything and have no local natural enemies. They threaten the entire invertebrate (i.e., insects, spider and snail) population and even attack small bird chicks.

They are so dangerous that when a small colony was detected on uninhabited Barrington Island, research station scientists felt justified in breaking their general rule against the use of pesticides and poisons. "We gave it the General Sherman treatment," MacFarland related. A space about the size of half a football field was cleared, dup up, burned and soaked with insecticide, watched awhile and soaked again.

It cost about $2,000. "You could say we saved that island from the fire ants, yes," MacFarland said.

Such diligence costs more than money. It is futile if the pests keep being reintroduced. Yet 7,000 tourists visited the islands last year, the 4,500 colonists move around routinely among them, and the scientists' aims are not universally accepted.

"We don't pay much attention to those guys. A man's got his own land, he can do what he likes with it," said Bud Devine, a grizzled Chicago native who has been a cattle rancher here for 29 years. There are 162 farms of various sizes on the four inhabited islands with about 7,000 head of cattle, he said.

"The science types, now, they're parasites really. They live off the tourists and donations from their foundations," Devine added, his voice dripping contempt. "They got nothing to do with us." He expressed interest in the feelers from large hotel chains and developers whose visions of making the islands a major tourist mecca give MacFarland nightmares.

The Darwin Station counters such attitudes with educational programs to convince the colonists their prosperity depends on preserving the undisturbed Eden that tourists come to see.

"Most income sources on the islands now are related to tourists, and the colonists have more money than they've ever had," MacFarland said. In 1960 not only were people not shooting the goats but they were introducing them to new islands; there's definitely been an attitude change in the last five years, he said."Kids don't stone the iguanas any more and the boat guides have all taken courses from us and they're pretty good."

Manuel Villacis, the cheerful owner of the 32-foot "Jesus de Gran Poder II" (Jesus of Great Power II), is one of the guides. Four of us, who had met moments before on Academy Bay's single dusty street, engaged Manuel and his blue and white converted fishing boat to take us around the islands.

Manuel and the six other boat owner-guides like him used to be divers and fishermen but make more money taking tourists around. Their boats lack running water, privacy or comfortable places to sit, and they smell of diesel oil as they chug along at the speed of the graceful porpoises that ride the bow wave, 7 or 8 knots. But the boats don't have to be reserved much in advance and they're the cheapest way to see everything and see it close up, closer than any group larger than half a dozen could possibly get.

We paid $66 per day, or $17 per person, for the five days and four nights we lived aboard the Jesus de Gran Poder II. In lieu of baths we swam daily in the cool sea whose color defines the word aquamarine. Manuel brought up langosta, clawless lobster, for three of our dinners; we forsook the cabin bunk beds for the starry skies on deck and woke at sunrise with our salt-caked hair like damp burlap from the dew.

But we stood toe-to-toe with blue footed boobies, eyeball to eyeball with giant cormorants and hand to paw and flipper with lizards, iguanas and sea lions.

That is just the problem. It is impossible not to reach out and touch, not to stroke the sea lion that wooshes into your lap playing tag underwater, not to want to feel the iguana's soft, dry skin, not to hold out your hand for the fearless mockingbirds, not to give the pelican on the poop deck a piece of banana.

Even with the purest of conservationist intentions, the firmest of beliefs that wild animals outht to stay wild and natural, unbothered by humans or their artifacts, it is impossible not to reach out and touch. It is just too awesomely wonderful to be so close, so accepted.

That has two consequences. Either the animals learn fear from being not touched but grabbed, or they learn to mooch. What is more unnatural than a three-foot-long, black marine iguana waiting for pieces of lunch from a hotel table, when it ought to be out diving for red seagrass? What is sadder than a terrified blue-footed bobby snagged on a trailing fishing line? And what is more thought-provoking than a yellow finch, one of Darwin's 13 varieties here, pecking away at a piece of plastic sponge on the boat-deck?

Darwin Station scientists are sitting out on the islands, under the shade of the weird cactus and the silvery trees, watching the tourists tickle the sea lions and pull the iguanas' tails. Guides like Manuel and others who shepherd the cruise ships' boatloads of 80 or 90 persons are required to keep their charges on discreetly marked paths that avoid the most sensitive nesting or mating areas. No food may be brought ashore, no plastic dumped at sea.

After seven years of study near the albatross nesting area on Hood Island, MacFarland said, "We can make a pretty strong statement that if the tourists are with guides and stay on the trail, there's no detectable effect up to now ont he albatross population."

Only 1/2 of 1 per cent of the Galapagos Park may be visited , and 80 per cent of the island's land area is included in the park, MacFarland continued. "The total number of animals exposed to visitors is really a very small proportion," he said.

There is a proposal before the Ecuadorean government to include the water around the islands - now free territory - within the park.Although there is no official control over private vessel movement on the water, effective control is exercised by the requirement that private sailors obtain permission to land from the Ecuadorean government on the mainland, 600 miles away.

The government recently stopped giving such permission because of past abuses, which islanders embellish into orgies of ant-infested plastic wrappers and cola bottles on remote islets as well as orgies of another sort.

But even with constant vigilance and effort, MacFarland has only dim hope that the animal threats will ever be totally wiped out Some threats can't be dealt with at all: "The main source of chemical contaminants is not from within the islands, but from rainfall and sea currents," he said.

With all that, the work continues. "We have a running chance to preserve it all and we have to try," MacFarland said. "Quality tourism is a valuable thing . . . just to demonstrate the thrill of what there is here and the value of trying to hold the line someplace in the world."