BONN — AS elegant black-and-white avocets feed on the windswept salt marshes of the north German coast, a judge at the European Court in Luxembourg will be asked today to step in to protect the rare and endangered birds. Judge Thijmen Koopmans of the Netherlands will hear an urgent application by the European Commission to order the West German government to stop building a dike in the Leybucht bay. The dike, it maintains, could virtually destroy the avocets' biggest breeding ground in Europe. The decision is expected next week.
The Commission is making use of European Community (EC) transnational laws designed to protect the continent's threatened migratory birds.
The outcome is being watched closely by West German conservationists, who fought for three years to persuade the Commission to take up the cause.
``For the World Wildlife Fund this is a test of whether EC laws on the environment can be enforced,'' says Holger Wesem"uller, WWF officer for the North Sea coast.
The Leybucht is one of the few bays on the continental North Sea coast that have not been dammed and drained to create rich farming land and to keep out the shallow, treacherous sea. Its salt marshes are breeding, wintering, or resting grounds for wild geese, ducks, and other sea birds who have been progressively robbed of this habitat elsewhere.
Such sea marshes are vital to the survival of the avocets, thought to number only 40,000, and to barnacle geese, who will fly in from Siberia in October to spend the winter there.
The avocets, who dredge up tiny creatures from the sea mud with their curious upturned bills, nest on the edges of the salt marshes, and as soon as their eggs hatch, take their chicks onto the mud flats to feed. In the autumn they move south to the coasts of Africa. The geese need the salty sea grasses that grow there to put on the fat they need for their return journey to Siberia in the spring.
The WWF and other groups have been fighting the huge, $100 million project for several years. By the time the Commission went to court last February, much of the dike had been built.
``That part is here to stay,'' sighs Folkert Everwien, a local environmental official and enthusiastic bird watcher. ``We will never get rid of it now.''
They now hope Judge Koopmans will grant an interim injunction to stop the rest of the dike. That part would cross through the main area in the northeast corner of the bay where some 2,000 pairs of avocets breed every year. Some 125 acres of marsh would be destroyed. The dike, Mr. Everwien fears, will bring people and noise close to the rest, driving the timid birds away.
EVERWIEN sees the dike as the product of an outdated mentality which goes back to the days when life on the Frisian coast was a constant battle between man and the sea, and nothing else mattered.
``This feeling is obviously so strong that people cannot shake it off,'' he says.
But times have changed. Politicians and the public have become wildlife-conscious. New laws, both national and international, give conservation groups weapons which they use to the hilt.
Now the role of ``villain'' has fallen to Theo Jansen, chief engineer of the Water Resources Office, whose job it is to preserve the sea defences and keep the land well drained. He has to solve three problems in the Leybucht, he explains: provide a higher, stronger sea dike, ensure the drainage of fresh water from the land into the sea now that two of the three sluices into the Leybucht are silted up, and provide a reliable channel to the sea for the Greetsiel's fishing fleet. They now only sail at high tide through a channel which needs constant dredging.
He insists that everything possible has been done to preserve the environment. ``Ten years ago I would have had to string the dike right across the mouth of the bay, destroying the salt marshes completely,'' says Mr. Jansen.
Instead he has brought it round the inside of the bay, except for a protruding ``nose'' tipped by a sluice that will provide a channel for fishing smacks and drainage water into the deepest part of the bay.
Thus the Leybucht will remain open to the sea and most of the salt marshes, he says, will be saved. New natural environments will form inside the ``nose'' and in a slice of farmland nearby which will be turned into wetland to compensate for what is being lost.
But conservationists are not satisfied. ``When you have only 40,000 of a species which can only survive in a very scarce environment, they are easily endangered,'' says a WWF ornithologist. ``Damaging the Leybucht breeding grounds is a very serious threat indeed.''