To the bafflement of marine mammal specialists across the country, an unprecedented number of dead or near-dead bottlenose dolphins have washed up on the Atlantic coastline from New Jersey to Virginia in the last five weeks.

"During normal mortality, they are dying at sea and getting gobbled up by sharks," says Daniel Odell, a research biologist at Sea World in Orlando, Fla.

But this summer the dolphins, who usually migrate north during the late spring or early summer and retreat to the south or out to sea with the approach of winter, have been washing ashore by the dozen.

Wild dolphins have long been a puzzle to scientists, who have been unable to determine the size of the dolphin population and what diseases the mammals encounter. And now, adding to the mysteries, is this sudden dying.

"I have been working with bottlenose dolphins for 18 years and have never seen them coming ashore in this shape, and smelling the way they do," Robert Schoel-kopf said Thursday from the Marine Mammal Stranding Center. The center operates a small, volunteer-staffed rescue and rehabilitation program in Brigantine, N.J., that handles beachings of marine mammals and sea turtles along the state's coast.

Dolphin strandings in New Jersey averaged three to four a year from 1979 to 1986, Schoelkopf said. But in the last 30 days he has responded to a record 47 strandings along the New Jersey coast.

The numbers, however, are changing so rapidly that Schoelkopf said, "I'll probably hang up the phone and have another one."

In Virginia, the southernmost state to report beachings of bottlenose dolphins, 45 have been found in five weeks, said Brian Gorman, public affairs officer for the National Marine Fisheries Service. The 10-year average, he noted, is only one a month.

According to James Mead, curator of marine mammals at the Smithsonian Institution, in that same period 39 dolphins have been found inside the Chesapeake Bay, one 40 miles inside the mouth of the bay; nine on Assateague Island and in Ocean City; two in Delaware; and 15 on the Virginia coast south of the bay.

One of the few barely living dolphins to wash up on the New Jersey shore appeared earlier this week at Brigantine. Retrieved by Schoelkopf, it was treated initially in the surf near the beach, then taken on a stretcher to the stranding center where it died three minutes later. There could have been no guessing, Schoelkopf said, that the dolphin had been alive "if you hadn't seen it die. There were sections of its body that you'd swear had been dead for days.

"I can't imagine these animals living as long as they have {in the water} in this condition," he said. "This goes way beyond anything I can imagine an animal going through -- there's really some suffering involved here. There is no way for them to maneuver in the ocean anymore. They are so weakened, they just go with the current and wash ashore. You look at them and you know there's something wrong."

The bottlenose dolphin -- familiar as "Flipper" in the television show and the one found in most aquariums -- has a lifespan of 40 to 50 years and is the most common of dolphins.

According to Robert L. Brownell Jr., chief of the marine mammal section of the U.S. Fish and Wildlife Service's National Ecology Center in San Simeon, Calif., "They are almost a worldwide species. They're found here in California, all over the East Coast, Mexico, Japan, South Africa. They don't occur in the cold waters of the Arctic or the Antarctic."

To help with the current dolphin crisis, Joseph R. Geraci, an specialist in marine mammal veterinary medicine and professor of pathology at the University of Guelph's Ontario Veterinary College, has been called in for consultation by the Marine Mammal Commission and the National Marine Fisheries Service.

Geraci and a team of scientists have set up a laboratory in Virginia Beach to investigate the mortalities there and in the Chesapeake Bay area. After arriving Thursday night, Geraci and his colleagues awoke yesterday morning to find eight more dolphins washed ashore along a 40-mile stretch of Virginia beach during the night. "We seem to be right in the thick of the problem," Geraci said.

The total death toll of bottlenose dolphins along the East Coast is "clearly over 100," Geraci said. "Somewhere between 100 and 120. But the reason I can't be sure is that as I'm talking new figures keep emerging."

As the deaths increase, the unanswered questions do also.

"There is very, very little positive data to go on," Mead said. The clues are few: "One, they are dead. Two, they are bottlenose dolphins," he said. "Outside of that, I don't know that there are any clues. The mortality started up rather rapidly in both areas -- New Jersey and the Chesapeake Bay area -- and just boggles at least my mind. I have never heard of any disease of this kind striking" whales and dolphins.

Mead said that "you can't rule out pollution and you can't rule out fisheries involvement. Those may play some part in it. I originally discounted pollution and fisheries, because this type of {mortality} pattern doesn't seem to fit them. But then, this pattern doesn't seem to fit any known diseases, so I leave those open as possibilities.

"If it were pollution, we would have expected to find mortality in other organisms -- birds and fish -- and we haven't . . . . If I were pressed to the wall, I would guess epidemic disease."

Geraci, like Mead, is ruling nothing out and making no preliminary diagnoses. Part of the problem for scientists is that the dolphins have deteriorated so much by the time they wash ashore that they are difficult to study.

"The animals are so dead that {the pathologists} can't do the kinds of tests they need to do, like viral cultures and bacterial cultures," said Odell, who spent four days in Norfolk last month investigating the phenomenon. "You really need incredibly fresh tissues and with post-mortem changes, a lot of things start happening that make it impossible."

The difficulty, however, is the accelerated decomposition of the carcasses, caused by the warm weather. "You lose a lot of information," Geraci said.

Striking dolphins of all ages and both sexes, the deaths are, according to Geraci, atypical in their very lack of pattern. "When these animals come ashore, there are usually trends. Whether it be that older animals come ashore or that very young animals who have been orphaned or have lost their way come ashore, typically we have a pattern."

The investigation of the bottlenose dolphin deaths is hampered by a number of other factors, including lack of knowledge about dolphins living in the ocean. What is known about dolphins, Geraci said, applies mostly to those held in captivity. "We know very little about their natural behavior and the conditions that affect their mortality in the species."

Although unprecedented for bottlenose dolphins, waves of deaths have hit other marine mammals, Geraci says. In 1979, Geraci investigated a large-scale mortality of harbor seals along the New England coast that was, eventually, attributed to an outbreak of influenza.