An attempt will be made to capture one or more sick, but still living, dolphins in an effort to learn what is causing the mysterious deaths of the marine mammals along the mid-Atlantic coast, scientists in Virginia Beach said yesterday.

Brian Gorman, spokesman for the National Marine Fisheries Service, said personnel and equipment from Sea World in Orlando, Fla., arrived in Norfolk yesterday afternoon aboard a Navy plane.

"We are anticipating within the next week that we will capture some live animals," Gorman said.

Access to a live bottlenose dolphin promises the marine biologists a far better source of information than the usually decomposed carcasses that they have been examining in the past week. Dolphins and other members of the order of cetaceans, including whales and porpoises, are protected under federal law; permission to examine a live animal was granted by the National Marine Fisheries Service.

"We may take some samples," Gorman said. "We may impound the animal briefly in a net and observe him. We really have not worked out the details. There may be more than one animal involved."

Dead dolphins continue to wash up along the mid-Atlantic coast, and one investigator said yesterday that the recorded death toll since early July is "certainly into the 200 range."

The estimate came from Robert J. Hofman, scientific program director for the Marine Mammal Commission, a member of the team of specialists that has converged on Virginia Beach to study the unprecedented mass mortality of the dolphins.

Test results have not returned from the National Veterinary Services Lab in Ames, Iowa, where tissue samples and cultures from several dead dolphins have been sent for analysis. "Some of the tests initiated on the first group of samples couldn't be completed because of the decomposition of material," said Robert M. Nervig, director of the facility. Test results on samples in better condition are expected within a few days.

In addition to the primary question of what is causing the die-off, scientists are trying to determine how many dolphins are dying and to what extent this blight represents a threat to the existence of the population. The base number of 200 dead dolphins is clouded by several factors: the possibility that some deaths are being reported more than once, and the unknown percentage of dead dolphins that are floating at sea or being eaten by sharks.

Not the least of the questions surrounding the dolphin deaths is how many dolphins there are on the mid-Atlantic coast. Joseph L. Geraci, leader of the Virginia Beach investigation, has suggested that a rough, but working, estimate of the bottlenose dolphin population would be 1,500.

James Mead, curator of marine mammals at the Smithsonian Institution, said no definitive number exists. Mead said the last data collected of the bottlenose dolphin population in mid-Atlantic coastal waters comes from the late 1880s, when there was a fishery for the dolphins. "Based on the catches of that fishery, there was a minimum estimate of 17,000," Mead said.

The degree to which mankind has decreased that number -- by interfering with the dolphins' feeding habits, for example -- is a matter of speculation. "We can't see any way that human activities would have helped the population," Mead said. "So we must presume that the number is somewhat less than 17,000."

But the specialists seem certain about one thing: If the diagnosis remains elusive, saving the diseased dolphins is "highly unlikely," Geraci said.

There is, he said, "no mechanism for injecting dolphins with antibiotics or vaccines. And in fact, that would be tampering with nature in a way that I wouldn't want to do. It's more important that we understand all of the environmental circumstances that have led to this problem. And if we have any control of those circumstances, we ought to exercise it in order to prevent this kind of thing from happening again."