Everybody loves dolphins, those playful models of animal wisdom, celebrated for protecting shipwrecked sailors and spending their days frolicking happily in the waves. Movies, television and water shows feature their antics. 

Nowadays, thousands of tourists swim with dolphins, captive and wild, with more signing up every day to commune with their animal intelligence. Most recently, a variety of organizations have sprung up that offer tours to places like the Florida Keys, the Azores and New Zealand, where participants can swim with wild dolphins and, brochures proclaim, experience emotional healing and spiritual awakening. 

But scientists, following a trail of bloody clues, are discovering that dolphins are far from the happy, peaceful creatures that humans think they know.

Growing evidence shows that the big animals, up to 12 feet long, are killing fellow mammals in droves, wielding their beaks as clubs and slashing away with rows of sharp teeth. Dolphins have been found to bludgeon porpoises to death by the hundreds. Unlike most animal killers, which eat their prey, dolphins seem to have murderous urges unrelated to the need for food. 

They have even been observed in recurring acts of infanticide. 

Off Scotland, a scientist watched in shock for nearly an hour as an adult dolphin repeatedly picked up a baby in its mouth and smacked it against the water, over and over, until it sank from view. 

Off Virginia, researchers found at least nine baby dolphins killed, their ribs broken, their skulls and vertebrae smashed. One small body bore puncture marks matching the pattern of adult dolphin teeth. 

"We have such a benign image of dolphins," said Dr. Dale J. Dunn, a veterinary pathologist at the Armed Forces Institute of Pathology in Washington, who aided the Virginia study. "So finding evidence of violence is disturbing." 

More widely, scientists and Federal officials worry about dolphins' injuring or even killing humans, especially given the rise in watching, feeding and swimming programs. 

"Wildlife can be dangerous," said Trevor R. Spradlin, a Federal dolphin expert. "But people see marine mammals differently, particularly dolphins. There's this misconception that they're friendly, that they're Flipper, that they want to play with people." 

Officials at the Commerce Department's National Marine Fisheries Service, where Mr. Spradlin works, have begun an educational campaign that sends out brochures to marinas, schools and fairs in coastal areas where people and dolphins interact, urging caution and warning of peril. 

"Dozens of bites have been reported," says one flier. "And people have been pulled under water. A woman who fed a pair of dolphins and then jumped into the water to swim with them was bitten. "I literally ripped my left leg out of its mouth," she said during her one-week stay in the hospital. 

Dr. Amy Samuels, a scientist at the Woods Hole Oceanographic Institution on Cape Cod, who studies interactions between dolphins and people, said injuries had been relatively minor so far. But she added, "Just because dolphins have a smile doesn't mean they're nonaggressive." 

In the United States, dolphin commerce is loosely regulated, and many countries have no rules at all. An American ban on feeding wild dolphins is routinely ignored by tour boats, which use food to lure dolphins nearby so people wearing masks and snorkels can swim among the creatures. And Federal rules on how to handle captive dolphins, completed last year, were suspended after swim centers objected to some provisions. Revised rules are not expected until next year. 

Many experts say tourist attractions will remain largely unfettered until a major accident occurs. 

"They're big, wild animals," said Dr. Andrew J. Read, a biologist at the Duke University Marine Laboratory who studies dolphin attacks. "And people should respect them as such." 

Of course, dolphin savagery pales in comparison with the brutality of people, who have managed to kill millions of dolphins while fishing for tuna. The dolphins, which breathe air, drown when large purse seine nets close over their heads. Fishery reforms seek to limit the slaughter. 

Closely related to whales, the 32 species that make up the dolphin family (Delphinidae in scientific nomenclature) include killer whales, which grow up to 30 feet long and are famous for their aggressive hunting pods. But the rest are smaller. The commondolphin is up to 7 feet long, and the bottlenose, up to 12 feet. Many dolphins have a pronounced beak and all have a central dorsal fin and sharp teeth for feeding, mainly on squid and fish. 

Significantly for humans, the mouths of many species turn upward in a perpetual grin.

As a result, the animals have long fascinated people. Ancient Greeks reported altruism in dolphins, saying they had rescued lost seafarers, and often depicted the animals in art. 

Dolphins are highly social and appear to communicate among themselves with a wide range of clicks, whistles and beeps, though scientists who study them say they do not actually have a complex language. Experts say dolphins are smarter than dogs andsimilar in intelligence to chimpanzees. 

The new-age dolphin operations go much further. In advertisements and tour promotions, they say dolphins are highly evolved spiritual beings. The dolphin's mere glance is enlightening, they say. 

"Dolphins reach deep into our souls, opening the door to our hearts," Marie-Helene Roussel said in an advertisement for her Delphines Center, on the Web (www.dolphinswim.com). Anyone with $1,600 can join her late this month on a six-day sail around Bimini in the Bahamas for "healing encounters" with dolphins. 

Her partner, Swami Anand Buddha, a former Louisiana lifeguard, says he found unconditional love, peace and bliss when he firstlooked into the eyes of a wild dolphin. "This," he says on the Web site, "is why I am working with people who are interested in exploring the potential of being transformed by love and higher intelligence of the dolphins." 

But now that image is being shattered as scientists document the grim slaughters. The research began around 1990 after large-scale deaths of dolphins and other marine mammals were discovered globally. 

In Europe and the United States, observation programs were started that sought the biological, ecological and behavioral secrets of wild dolphins. At first, a virus was implicated in many of the deaths. 

The first clues to the deliberate killings were found on a large bay on the northeast coast of Scotland known as the Moray Firth, an arm of the North Sea, by Dr. Ben Wilson, a dolphin expert at the University of Aberdeen, and Dr. Harry M. Ross, a veterinarian at the Scottish Agricultural College. They focused on harbor porpoises, marine mammals up to five feet long, that were turning up dead with a strange mix of injuries, including multiple skeletal fractures and damaged internal organs. 

Suspects included boats and fishing nets. But in 1994 the researchers discovered a newly killed porpoise, its flank torn by bloody tooth marks -- marks that perfectly matched the 0.45-inch spacing of the teeth of adult bottlenose dolphins. 

"It was, 'Oh my God, the animals I've been studying for the last 10 years are killing these porpoises,' " Dr. Wilson recalled. 

Other evidence quickly fell into place. Of the 105 porpoise post-mortems the team had done on animals found around the bay from 1991 to 1993, 42 showed clear evidence of dolphin attacks. 

The case was much strengthened after the team began finding people who had witnessed dolphin attacks. Observers twice saw the porpoises escape. Two apparent killings by a group of dolphins were captured on videotape. 

In 1996, the team published its findings in Proceedings of the Royal Society, a British journal. "These findings challenge the benign image of bottlenose dolphins," they said. 

But still they did not know why the dolphins killed. Perhaps porpoises and dolphins competed for food, the scientists reasoned, or perhaps the porpoises were seen as a threat to young or ill dolphins. 

The killings of dolphin calves only deepened the riddle. The victims were roughly four feet in length -- about the same size as the dead porpoises. In all, the team found five dead dolphin calves with fractured ribs, ruptured lungs and spinal dislocations. 

Again, witnesses and videotape aided the hunt for evidence. In one case, Dr. Wilson himself watched in amazement for 53 minutes as a calf was hit, seized and butted into the air by an adult bottlenose dolphin. 

In all cases, the aggressor's sex was unknown. But the scientists speculated that the killers might be male dolphins trying to destroy rival offspring and free up females for mating. Females, the researchers say, become attractive to males within a few days of losing a calf and apparently, when tending youngsters, stay sexually inactive for years. 

Infanticide is common in nature. Females kill their young when food is scarce and male lions and bears, for example, sometimes kill the young of a female taken as a new mate, giving them a reproductive and evolutionary edge. 

The Scottish scientists published these new findings last year in Proceedings of the Royal Society, saying it was "the first evidence of infanticide in cetaceans," the scientific grouping for whales, dolphins and porpoises. They speculated that the assaults on porpoises might develop "skills used in infanticidal attacks," or alternatively might stem from simple aggression or sexual frustration. 

Meanwhile, an American group was independently making similar discoveries as dead porpoises and baby dolphins were washing up along the Virginia coast, many with the telltale internal wounds. Suspicions were first aroused in 1997 when a baby dolphin was discovered with bruises, broken ribs and a lacerated lung. A check of specimens in 1996 and 1997 revealed eight other unusual baby deaths. 

"Only one had a bite mark," recalled Susan G. Barco, a research scientist at the Virginia Marine Science Museum in Virginia Beach, Va. "And the distance between the teeth matched that of the bottlenose dolphin. There was no evidence of shark bites or boat damage." 

In addition to Ms. Barco, the Virginia group includes Dr. Dunn of the Armed Forces Institute and Dr. Ann Pabst and Dr. William McLellan of the University of North Carolina at Wilmington. 

Dr. Read of Duke University, a porpoise expert who is aiding the Virginia study, said evolutionary factors seemed a likely explanation for the infanticide. The porpoise deaths, he added, were harder to understand. The two kinds of marine mammals eat different fishes, he said, so food competition is unlikely. "And there are very few instances when one mammal kills another when there is no risk of predation," Dr. Read added. 

The emerging consensus is that wild dolphins can be cold-blooded killers. 

Federal officials say dolphins pose little threat to people in captive swim programs, where the animals are usually well-trained and closely supervised by experts working in pools and enclosed bays. During the past five years, the number of such businesses have risen to 18 from 4, said Dr. Barbara A. Kohn, a veterinarian at the Department of Agriculture's Animal and Plant Health Inspection Service, which oversees the field. And more such tourist attractions are planned. 

Through 1994, Dr. Kohn said, statistics showed that the injury rate was less than 1 in 10,000 people. 

"That's pretty good," she said, adding that no serious injuries had been reported since then. "So it continues to be fairly safe." 

The danger, experts agree, is when people swim with dolphins in the wild, an increasingly popular, unregulated sport. For instance, Panama City, Fla., has a half-dozen boats offering such adventures. 

"It's a time bomb waiting to go off," said Stephanie K. Dorezas, a spokeswomen for the National Marine Fisheries Service, which oversees dolphins in American coastal waters. 

Federal officials say the recent scientific findings about wild dolphins and recent mishaps with the big animals are giving the Federal warning campaign a new degree of urgency. 

"We're not trying to prevent people from going to the beach or going on dolphin watches," said Mr. Spradlin of the fisheries service. "But they need to do it safely and responsibly. It's like bird watchers or people on safari. That same kind of caution and respect needs to be applied to sea life." 

Copyright 1999 The New York Times Company