Polluted North Sea site of seal rescue effort. SAVING THE SEALS

Lies Vedder has taken care of abandoned baby seals for 11 years. This is the first summer the Dutch veterinarian hasn't enjoyed her job. A mysterious blight is sweeping down the North Sea coast from Denmark to the Netherlands, killing hundreds of seals in its path and causing an environmental crisis. So far this summer, nearly 2,000 seals have died - out of a total population of about 13,000. In some parts of Denmark, up to half the herd has been decimated. And in Germany, emergency centers have been set up to deal with sick animals.

Scientists aren't sure whether pollution plays a role, but it certainly doesn't help. The North Sea is one of the dirtiest bodies of water in the world. Every year, more than 11,000 tons of heavy metals and 5 million tons of treated sewage are dumped into the sea by surrounding countries. Much of the waste flows into the sea through heavily polluted rivers, such as the Rhine and the Elbe.

Researchers studying the seals believe a virus is causing the blight. This means that it could have nothing to do with the condition of the water. But scientists are investigating whether pollution could be contributing to the problem - by weakening the seals and making them more susceptible to health problems.

``The seals tell you what is happening in the environment,'' says Ms. Vedder. ``They are at the end of the food chain.''

Vedder, who works in a privately run seal sanctuary in this quiet Dutch village, says the animals were in bad shape long before the current problem appeared. In the mid-1970s, scientists discovered that polychlorinated biphenyls, known as PCBs, and other dangerous substances were settling in shallow coastal regions and inhibiting the seals' reproduction.

The Dutch launched a program to try to bolster the seal population. The use of PCBs was halted in the Netherlands in 1983. The coastal zone - known as the Waddenzee - has also been put under close protection. But Holland wasn't able to entirely stop the flow of PCBs into its coastal waters, since the Rhine carries this and many other dangerous materials from deep inside Europe.

At the same time, the Dutch sought to increase the survival rate for the seals that are born. During the annual birthing season - which peaks this month and runs into August - boats comb the Dutch coast in search of baby seals that have lost their mothers.

Even under normal circumstances, the death rate for baby seals is very high. If a group of seals is suddenly frightened, for example, the animals will scatter in all directions. Babies can lose their mothers in the confusion and never find them again. These young animals are known as ``howlers'' - since they'll often lie on beaches crying for their mothers. Because seals won't adopt another's young, the animals would normally die.

Under the Dutch program, abandoned seal pups are picked up and taken to Pieterburen, where they're nursed until they're ready to return to the wild. The center is the only such facility in Europe and has taken in orphans from as far away as Greece.

``The only thing we can do is try to figure out why the seals are becoming infected,'' says Dr. Fritz Dieterich, an environmental protection expert with West Germany's Environment Ministry.

In Pieterburen, researchers are hoping to learn as much as they can from the baby seals. The center normally takes in 30 infants in a summer.

This year, they passed that number by the first week of July. Many of the infants are arriving in extremely poor condition. Mother seals, weakened by illness, have given birth to an unusual number of premature babies. Other baby seals are being born to sick mothers who are too weak to care for them.

The problem has jolted governments throughout the region. In West Germany, where the seal deaths have become the media sensation of the summer, there's been a sudden push to end all North Sea dumping.

West German Environment Minister Klaus T"opfer, while refusing to link the seal deaths to pollution, has pledged to end his country's offshore dumping of chemical wastes by the end of 1989.

But it will take more than a few countries' efforts to turn the tide.

At a meeting held last year in London, eight countries bordering on or near the North Sea argued over whether there was sufficient proof that pollution of the sea was significantly harming marine life. Some scientists contend the North Sea's real problem is overfishing.

The seal disaster, along with several other troubling environmental problems, such as an enormous algae bloom earlier this summer which threatened to wipe out fisheries in the Skagerrak Sea, may increase pressure to take action.