WEARING designer sneakers and a stylish back pack, the lady from New York stops along the rocky trail and peers down at a nesting blue-footed booby a mere two feet away. "Hi," she says in a cheery voice, "are you sitting on some eggs?"Cheeriness was not Herman Melville's reaction when he visited these brooding, mostly volcanic islands in the 1830s. "Little but reptile life is here found," he wrote with contempt, "the chief sound of life is a hiss." It took the patience of a Charles Darwin to get beyond the hissing. He found the extraordinary biological wonder of the flora and fauna of one of the earth's rarest places. "It was most striking," he wrote of his five-week visit to this archipelago in 1835, "to be surrounded by new birds, new reptiles, new shells, new insects, new plants." Which brings us back to the lady from New York looking down on the booby with the blank stare. The lady is herself a species: a not-so-rare "ecotourist" or "nature tourist" or "ecotraveler." Her motive for travel (if not her appearance) is in character with that of Mr. Darwin: to experience a unique habitat in the world where man has done little to alter a pristine state. For this reason, and because of heightened concern for the environment, the concept of ecotourism over the last five years or so has become a big seller for nature-oriented tour companies. Most countries, especially in the third world, want the revenue generated when they preserve unique habitats for ecotourists rather than permit oil exploitation, agriculture, or killing of wildlife. It's called "sustainable conservation." For instance, the World Bank determined in 1973 that a wild elephant herd in Kenya's Amboseli National Park was worth $610,000 a year to tourists willing to pay to see it, in contrast to natives killing it for tusks. The ecotourist for the most part rejects the "sun and fun" tourist experience. He or she wants to be in jungles, rain forests, deserts, on wild rivers, at the Arctic Circle, Baja, Nepal, Patagonia, Galapagos, or close to wildlife on the African plains. Educational adventure is the lure. The cost to get there is higher than most tourist resort packages designed for amusement, but the benefits are close to the heart, exhilarating and unforgettable. And, my, how the cameras click. A guide watching a dozen ecotourists on the Galapagos taking photos of seals said wryly, "The males work for Kodak and the females work for Fuji." Ecotourists also like the idea of traveling with the least amount of impact on the habitat and culture they are encountering. Walk carefully, take only photos, spend with the local economies, and help save a beleaguered planet, says the ecotourist. But despite this professed sensitivity to the environment, and the genuine care of some tour companies in conducting ecotrips, the growing number of ecotourists and mainstream tourists are presenting the earth with a critical dilemma: Too many people are traveling everywhere in the world. An estimated 400 million arrivals occurred in countries throughout the world in 1988. The result: What ecotourists (and any kind of tourist) want to see, experience, and save is often in danger of being loved to death. A report by the Organization for Economic Cooperation and Development a decade ago concluded that "tourism destroys tourism" in certain regions. Examples of too much tourism can be found on every continent: * In Kenya's Amboseli National Park, more than 200,000 tourists a year speed through the park in vans chasing animals, disrupting feeding habits, and destroying underbrush. The once lush area has been described as a "moonscape." * The World Conservation Union said last year that tourism is devastating the world's coral reefs. Of 109 countries with reefs, 90 are being damaged by sewage from hotels, anchors from cruise ships, tourists breaking off chunks of the reefs, and by commercial harvesting for tourists. * So many tourists visit Stonehenge each year that the site is now encircled by a fence and a traffic signal nearby controls the flow of buses and cars. * In Nepal, 120,000 trekkers a year deplete forests by using wood in lodges or houses for baths and cooking or by buying it from locals. Few trees are left in the Annapurna Sanctuary, thereby destroying a wildlife habitat. * The Galapagos Islands, long considered a model for controlling the flow of ecotourists, has seen the number of visitors increase in 10 years from 10,000 to around 45,000 per year. Social and ecological problems are increasing throughout the archipelago. "What we are seeing [in Galapagos]," says Dr. Craig MacFarland, the president of the Charles Darwin Foundation and a specialist in wildland planning and management, "is a trend that if not corrected will lead to something like we have in Hawaii, where 60 to 70 percent of the original flora and fauna is gone, wiped out. "The tourists don't know it, but you don't have ecotourism today in Hawaii; what you've got is tourism." Correction, or at least a course adjustment for the Galapagos, may be on the way. At the direction of President Rodrigo Borja Cevallos of Ecuador, a commission was established last August to shape the future direction of the Galapagos. To stem the flow of ecotourists, President Borja also put a temporary moratorium on granting permissions for new tourism operations. Dr. MacFarland, who has had 20 years of experience working in Galapagos, applauds the effort, although he notes there have been at least five other commissions in the past. "This time," says Dr. MacFarland, "once the plan is completed, the future of Galapagos will depend upon the willingness and ability of [all the key players] to convert what has been a 'game' of power and vested interests into a truly collaborative effort for the good of all involved." The reason the Galapagos can generate an estimated $180 million a year for the Ecuadorean economy is the incomparable experience the islands offer to visitors. At a cost of around $2,600 for a week to 10-day visit, usually including air fare, ecotourists travel in groups by boat from island to island. They walk among the blue-footed boobies, sea lions, marine and land iguanas, albatrosses, pelicans, finches, and frigate birds. Snorkeling will bring an ecotourist face-to-face with a rainbow of fishes and frolicking seals. On the grounds of the Charles Darwin Research Station near the town of Puerto Ayora on Santa Cruz Island, you can lean down and scratch the leathery, crenulated neck of an appreciative giant tortoise weighing 500 pounds. He looks back at you with ancient, black eyes, a slow, prehistoric presence at your fingertips. "What first drew me here," says Godfrey Merlen, standing among a few seals at the shoreline of a cove on Floreana, "was the extraordinary, primitive nature of the place." Mr. Merlen, a biologist, has lived on the islands for about a dozen years and is the author of a guide to the fishes of the Galapagos. "Tourism has its good side," he says, "and one hopes that people leave here with a very positive feeling for the wild world." Each wild island, formed by volcanic lava or geologic uplift, is marvelously different from its neighbor in colors, plants, creatures, and landscape. "I never dreamed that islands, about 50 or 60 miles apart," wrote Darwin, "and most of them in sight of each other, formed precisely of the same rocks, placed under a quite similar climate, rising nearly to equal height, would have been differently tenanted." Most tour boats follow the pattern of traveling between islands at night while the engine either drums you to sleep or brings a fitful night until you acclimate yourself. Breakfast is at sunrise. All boats have a trained guide or naturalist aboard to tell as many details about the islands as possible. You are taken ashore in a pangra or dinghy. But as fascinating as the details are, and as close as one gets to the creatures, the impact on this writer was the realization that everything here is young in geologic time - and still evolving. Some islands are from 3 million to 5 million years old, mere pups in geologic time. What these young islands face now is a tug of war between the environment and economics, perhaps more stressful than any volcanic activity. It is a conflict being played out all over the world. "My view is that there has to be biologic considerations before economic ones," says biologist Merlen. "It's all involved in small plants and insects and seeds which form a complicated web of life. "The individual sea lions have very little do with it. And so to understand the details, it's something much more than going from island to island and viewing things in a very superficial way. Who knows what will happen to tourism 20 to 50 years from now?" Oswaldo Munoz, owner of Nuevo Mundo Expeditions, a Quito-based tour company, contends tourism has aided in conserving the islands. "Many responsible and well-established tour operators have taken key groups to the islands," he says. "We have played a very important role in finding funds and in technical assistance because of the kind of people we have taken to the islands. We continually work with [environmental organizations] to promote preservation of the islands."