NEW YEAR'S DAY walks along 30 different parts of the nation's seashores were an appropriate way to begin what has been designated as "the year of the coast." Coasts are ideal for walking and meditating -- many of them, anyway -- and much meditating needs to be done to be sure they keep their charms.

Some of the problems are obvious. The conversation groups sponsoring those New Year's walks had no difficulty finding sections where litter or industrial and commercial development or fencing off by private owners intrudes on public enjoyment of that always intriguing seam of land and water. These problems can be eased if people will help nature along by carrying away their litter and if government will protect and expand the undeveloped portions of the shores. Since three out of five Americans live in counties bordering the shoreline (if you count the Great Lakes), the need for greater pulic access is clear.

But other problems of the coasts do not yield to such clear solutions. The oceans are rising ever to slightly each year; that change, couple with the natural forces of wind and waves, is eroding substantial portions of coastline. In Virginia, for instance, some 28,000 acres of land have been surrendered to the Atlantic Ocean and Chesapeake Bay in the last century.

Some of this erosion can, and should, be halted. That's where cooperation between federal, state and local authorities through the coastal zone management program is essential. No single property owner, acting alone, can long hold back the sea. Even the state and local governments, which are traditionally reluctant to cooperate in such projects, are beginning to realize that.

But the major difficulty is deciding which projects are worth doing and which are not. Last year, for example, proposals were made for major projects to facilitate development on Hatteras Island and to stabilize the location of the Oregon Inlet through the Outer Banks. Given the unsuccessful experience of the National Park Service in trying to stop beach erosion at nearby National Seashore, the latter effort seems likely to fail or to produce some totally unexpected and undesired result.

Development on Hatteras is precisely the kind of undertaking the government should oppose. Additional development in fragile and changing coastal areas will inevitably lead to additional demands for protecting that property from the forces that cause the change. In some places along the coasts, the country will best be served by leaving nature alone.