Late March is one of the twelve best times to head for the beach; early April is another. Spring is in the inland air. The first terns are coming in, about to stake out their breeding grounds and nest sites. Curlews too, and dunlins, black skimmers and oyster-catchers.

Rock fish -- stripers farther north -- are just appearing offshore, a friend tells me, and fishermen are on the verge of trying for black drum. Perhaps the sea rocket is about to sprout along the dunes.

There's no telling what exactly will happen this time of year along the coast between the mouths of Delaware and Chesapeake Bays -- a range of ocean coast within four hours of Washington. We went to see and proved that simple rule; I've never failed to find something new, or to be reminded of some forgotten lesson. When summer people pack up to go, they say, "I can't wait. It'll be just like last year." To the contrary, I find it always different. Expect the unexpected. Some sophisticates head for Aspen or Cozumel at the drop of a name, I go to the beach.

A few winters ago, over cafeteria coffee, a young and unhappy friend complained to me, "I don't know what to do. My brother's in Intensive Care, my boyfriend left me, and my shrink's on vacation." Was it a Woody Allen put-on or a catalogue of modern despair? Either way, I said "Go to the beach," through it was December. "You'll have the place to yourself. No distractions but surf and birds. Pick a sunny, windless day and you can swim; the water's warm from summer still." "The lady's troubles were real. She took the trip -- to Bethany, I think -- and returned literally refreshed, ready to face whatever came her way again.

The beach is an all-year place to go -- sometimes for rest, for natural revelry, for recreation or respite. A week ago my wife said, "What do you want to do? Our taxes are almost ready and the kids are away this weekend." "Let's go to the beach," I said. Last weekend wasn't early spring along the Delmarva coast between Cape Henlopen and Cape Charles: It was only the last of winter. We saw proof looking northward from the bridge that soars over Indian River Inlet. From there the Delaware beach was barely visible. Surf washed nearly to the foot of the manmade dunes, undermining them in steep little tumbles, seeming to promise to take the beach grass next, then the dunes themselves, then the swale and soon the road itself.

Soon? With the next high tide pulled higher by the next full moon? With the next northeaster or hurricane? Probably not till then at least -- whenever that will be -- because what we saw on Saturday was the pinched face of a winter beach, a different place from the broad summer strand because of seasonal weather and waves.

Wintertime's heavier seas rob the beaches along this coast. Big waves, driven by winter storms, strike the shore. Breaking against the land, they wash back seaward, heavily carrying sand away. The beach becomes steeper as a result, and more sand washes off its face with each new wave. The progression continues as the beach becomes actually narrower. But with the return of gentle weather over the Atlantic, where the storms rage that send the waves toward shore, the process reverses.

Ocean currents carry sand from under water lodes to the sandbars near shore; inshore currents pick up the sand and, as waves break on the spring or summer beach, they leave new grains. So the beach builds out again, and with a gentler slope. Ech wave brings a little more sand than it takes away, and the beach builds its hospitable summer profile. At Ocean City it was hard to tell the time of year except to say it wasn't summer. Only dozens of people walked the boardwalk and only a few pairs were on the sand itself. There are parking places for the asking in every block. The only "no vacancy" signs were left by accident when some smaller motels and guest houses closed last fall. Restaurant reservations? I doubt you need them at this time of year. Ocean City Summer Folks Beware: You won't know the place without the crowds. our real destination was Assateague, a long barrier island that stretches from the Ocean City Inlet for more than 30 miles, into Virginia. The northern end of the National Seashore there has just grown six miles, in effect, the result not of a natural phenomenon but of a legal one.

When the National Park Service took over, it offered landowners the choice of selling outright or occupying their land and taking less money in the end. So the northern tip could be reached only by boat. One owner of a three-mile stretch elected to stay on ten years, and his lease has just run out. Now, for the first time, the entire northern stretch of island is accessible to hikers from the parking lots near the park headquarters at Berlin. This part of the island will be left nearly wild; no RVs, thank you. You'll see nothing more alien to nature there than the view of Ocean City on a clear day.

I'd traveled the stretch before, but in a Jeep with an orithologist studying peregrine falcons, which migrate the length of Assateague each fall. (Even when one goes beaching to study the fastest creatures ever to inhabit the earth, one sees surprises. Early one morning we spotted an injured gull as we drove north. Coming back again, we drove around a small dune and flushed a huge brown bird -- an immature bald eagle, its head not yet crowned in white. It raised its head from breakfast and spread its wings seven feet across in the same motion, then wheeled into the air from a standing start with mighty grace -- leaving the dead gull on the sand. I'd never seen an eagle's yellow eyes alive before." Last saturday we saw nothing larger than a gull, and few of those. We didn't see Ocean City's towers and honkytonk from Assateague, nor even the horizon, the feature that so often gives perspective. We saw mist change to rain and back again to fog that brought a gray and eerie beatuty to the shore. We saw dunes that looked as high as desert mesas from twenty paces, their brows carved by the dying winter's winds. Then five steps closer they came into sharper focus, shrinking in an instant to only ten feet tall. Yes, eerie.

I'd meant to take Mary south, to the Virginia end of the island where January tides broke through the barrier dune and threatened the narrow road. Waves washed toward the sheltered bay, perhaps a sign that Fishing Point will become an island soon -- another event in the endless chain of the shore's inexorable life. Alone one stretch, the surf had laid bare the old reed-tangled mud that proves that this island once lay farther east. (Barrier islands migrate slowly toward the land, rolling over the bays and marsh they once protected.) Now the gentler waves are covering the ancient mud with sand again, and the point itself -- perhaps the future island -- builds farther out at an apparent pace of a hundred yards a season.

The sea robs, the sea creates. Halfway up the island I had tracked across overwash fans of sand alone and felt myself in another littoral world. Where the dunes are intermitent, last winter's storms blew water up the brow of the beach and through the breaches. The water went its way, leaving layers of sand inches deep spreading behind the outher dunes -- new sand to be anchored by colonizing beach grass. But we didn't get that far south on Saturday. We walked the island's upper end.

The dunes there showed signs of the changing year. Winter winds carry light particles of sand away; white quartz sand blows inland or elsewhere, while heavy black magnitite remains in smudges broad as skating rinks. Now wind is blowing new white sand back in little windrows to form rippling zebra stripes up the face of dunes.

We didn't see the oyster-catchers, but they'll be there soon -- black-and-white, big-bosomed birds with scarlet bills to peck out the innards of live mollusks. We saw no black skinners that fish on the fly, pushing the water with their lower bills to snatch up minnows. We saw no terns, but they'll be coming soon as well to breed and lay their eggs on the open beach. (A word of warning: When the birds are nesting, please stay away. Shore birds sit on their eggs and shelter their chicks not so much to keep them warm -- but to keep them cool and shaded from the sun. Pause near a nesting site and the parent birds will fly away; a human's picnic time is long enough for the eggs to cook. Then again, some terns mob intruders and stab their scalps with their sharp bills. So for the young birds' sake, or your own, stay away from nesting birds.)

Through the fog we saw herring gulls enough, and a rare tableau. At Cape henlopen I've seen a frightened deer flee across the open beach, splash into the surf and head for Cape May, New Jersey. (Deer are known to swim long distances across shallow ocean water -- especially when chased off their old range by men or dogs.) On Saturday the deer we saw were peaceful: A pair of whitetails browsing in the lee of the outermost dunes, veiled in clouds of fog.

What was there for them to eat? Saucer-sized medallions of a colonizing plant, lovely yellow in the center and spreading outwards to green. We saw the first gren sprigs of beach grass growing straight and fine-tipped. Spring was coming -- perhaps it's there today. The sky tried to clear. We walked a few miles among the dunes and along the beach face cluttered with broken reed, and the skeletal shapes of driftwood. The dunes seemed lunar or labyrinthine in the fog. We found a snow goose drowned, its bony bill serrated, nearly having teeth.

We didn't regret being too soon for glowing spring, too late for the fury of winter at the shore. The year seemed snared on a fence, caught between seasons. Winter was dying as new sand covered black smudges; spring tried its best through the inner shoots of beach grass. We were right on time for a motionless center of some solarcentric wheel, it seemed.

The sun nearly pierced the sky, then the fog closed in again and we turned for home.