FACE IT: Everyone who willingly stays home all summer in this climate has lost his reason or caught a case of the glues. (Perhaps his brain cells poached last August.) The end of the land lies three hours away as the Mustang trots. A bus ticket as far as buses go due east costs less than a parking ticket and you can pack your lunch. Between Sandy Hook, New Jersey, and Ocracoke, North Carolina - both within a day's ride in these mobile times - there are 1534 miles of sandy seafront, says the Army Corps of Engineers, and fifty islands at least twice the size of the National Zoo. There's action or utter idleness for every taste: quiet by-the-week cottages at Bethany Beach, the Coppertoned crowds of Ocean City, the fishing tides of Nags Head, the wild isolation of Virginia's hard-to-reach barrier islands. Something, in a word, for anyone according to schedule, budget and fantasy. There are old people, young people, solo people, no people; discos and dunes, beer, bugs, birds, bushes and bivalves on the hoof or between Wonder Bread rolls. Where to stay? In a Jersey-Victorian summer palace, a tent you pack in to Assateague, a highrise Virginia Beach motel.

How many beaches are there along the mid-Atlantic shore? Some 200, defined by our names. But in natural terms there is just one. It stretches from South Carolina to Rhode Island, 700 miles as the croaker fins and seven times that far if you walk every foot of coast.

The mid-Atlantic beach is a fairly distinct entity. To the north, glacier-made New England's hard-rock coast supports another kingdom of plants and animals that thrive among stone. To the south, climate, sand composition and natural populations become significantly different. Look at a map of the Atlantic Coast: the sea does not strike the mainland's edge here, as both northern oceans pound the west coasts of America and Europe. This coast is almost entirely composed of barrier islands, no matter how much man has done to camouflage that fact.

Starting parallel to Long Island, constantly changing sand islands are the rule. Though often linked to the mainland by low-tide bars, natural isthmuses or artificial causeways, barrier islands constitute the New Jersey coast, the Delmarva Peninsula and the Outer Banks. Between, behind and among them - protected by the ocean's raw force - lie inlets, bays, sounds and lagoons lined by uncounted marshes, a realm of astonishing ecological importance to human and marine life. The marsh is as much a part of our coast as the sand.

Between the surf and terra firma (no land the sea touches is very solid) lurks a bewilderingly complex place. The beach tangles geology, botany, zoology, weather, physics and oceanography all together like a surf row of seaweed, six-pack plastic, spider crabs and tidal lint in the fishnet of natural science.

Energy and change are the only constants in this ribbon of a region where old, sloping land meets the kinetic ocean. This shoreline, from a few yards to miles wide, is the result of a movable object meeting the primeval irresistible force. (The ocean is presently winning as its level rises an inch a century, but the next ice age will take it all back, if you can stick around.)

This is the account of a nature trek from Delaware to North Carolina:

At the northeast shoulder of the Delmarva Peninsula is Cape Henlopen and a state park where I saw two-toed hoof tracks in the sand several springs ago. Deer forage in woods and marsh near wild beaches but usually stay hidden from human day-trippers. Then I saw a small white-tail scamper around a dune and head into the surf. Though a slight sea was running, the animal swam toward where Cape May lurked a dozen miles across Delaware Bay, hidden beneath the low sky. Yes, deer swim to reach islands or elsewhere.

An easier way to go northeast is by the ferry plying between Lewes, Delaware, and Cape May, New Jersey, which shelters one of Roger Tory Peterson's favorite birding spota. Many birds are reluctant to cross water they can't see across, so the south end of a land mass like New Jersey is something of a migratory bottleneck, according to Smithsonian ornithologist George Watson.

Turning south from Cape Henlopen, wild and settled stretches are interspersed. The coast road runs straight down the barrier islands between a plain of bracken on the left and the meandering bays. The sea is hidden by a line of man-made dunes; the snow fences that collected them grain by grain stand buried to stubs in the sand. There are World War II watchtowers, and widely spaced parking lots. At the Indian River Inlet, where rock breakwaters guard the channel and fishermen go on foot, the road arches over a bridge tall enough to let the charter boats apss beneath with their outriggers erect in the sockets.

Then, on this island of shifting sand, the condominiums of Ocean City rise ahead: towers, pyramids and monoliths, some standing barely fifty feet from the high-tide line. The beach is eroding here, as it has for years, and bulldozers pile up the sand in a steep, uneven line of dunes, a wishful dike against the inevitable storm surges. (Experts say it's chancey at best. Certain strong storms will breach dikes like these, says a prominent geologist, "and Ocean City just doesn't have enough little Dutch boys." He wonders when a condo, its footings awash, will fall into the sea like a Douglas fir.)

Further on, the skyline drops: several-story concrete block motesl thrice as wide as high, and wooden ones a generation older. The cross streets number into the hundreds. This is a city of human amusements. In a bar at sundown a pretty legal secretary and a handsome engineer said they loved the town. They came all the way from Seattle and Annapolis respectively "just to have an affair," and it was going swimmingly. For people who like "action" or anonymity, this must be the place.

Back across the southern causeway signs point to Assateague National Seashore headwuarters at the upper end of a thirty-five-mile island that was saved from development - and just as well. Robert Dolan, whose beach reached convinced authorities to stop trying to stabilize the Outer Banks, says the north end of Assateague has moved west 1.3 times its original width. The planned house lots are under the Atlantic now, though the island remains seemingly intant. It simply migrated. Erosion along the entire east coast islands naturally proceeds at a few feet a year. "There'll always be a beach," says another geologist. "It just might not stay where it was or be where someone wants it."

A few miles down island chief interpreter Larry Points stops along the beach by a stretch of old macadam, a remnant of road from the once-intended summer town. Only a few rods of pavement remain, crumbling at the edges and cracked clear through. Behind it a tall dune rises, covered with American beach grass on its seaward side. This unique plant can survive constant salt spray but can't stand the competition of faster-growing grasses that thrive in gentler environments. Possibly stimulated by sand gathering around its stems, it sends out rhizomes, runners tht sprout up, which in turn collect more sand and slowly build the dune.

The dune, in turn, protects other plants that secure the dune's landward side. Below it grows an impenetrable thicket: elder, holly, bayberry bushes and loblolly pine. None grows taller than the dune because salt spray blowing off the sea keeps these trees pruned back. A chunk of dune side has slid away revealing strata of dark sand, heavy garnet and magnetite. These minerals become concentrated in black layers when fierce winds blow away the lighter grains of quartz that were mountains geological ages ago.

Along the beach are the constant raucous birds: laughing gulls, herring gulls and ring-billed gulls; busy sandpipers and their vocal kin probing a living from the wet sand. There are the remains of many kinds of shells: crabs, clams, sea snails.

Like every natural shore, this sanctuary is alive. Ocean water is a cold soup of tiny nutrients. Microorganisms live in the open oceans and in the minute channels of water among sand grains wherever the beach is wet. In one respect the living is easy. Many little animals learned to put up with the oceanic headaches of constant pounding for the sake of limitless free meals served by the tidal caterer. The small animals might grow complacently fat, but they must spend their lives evading larger animals that learned to feed on them. Eventually even the largest of these ends up piecemeal in a sea soup, so the cycle continues. The secret of each species is that it has found a niche - adapted itself to the environment's physical rigors in order to take advantage of the plentiful feast long enough to reproduce.

One can walk to the south end of Assateague or drive the long way round - down Route 13, then across miles of marsh, to the low island of Chincoteague.

It's a curious place where the traditional livelihoods survive tourist seasons. Clapboard tourist homes take in paying guests a clam shell's toss from packing houses. Off-shore dredgers and seiners dwarf the sport-fishing boats alongside the bulk-head.

Stands selling painted shells and clam sandwiches line the road northeast of town. The marsh begins again, patrolled by "cranky birds" - herons - afoot and a-wing. Beyond an unmanned toll gate there's a noisy wood-planked bridge over the tidal gut to the Wildlife Refuge and south end of Seashore. Sandi Hellickson, a Park Service ranger and naturalist from North Dakota, reports a harbor porpoise came ashore last week. The books say it ranges from Greenland only to New Jersey, which is two states north.

She can tell the dried droppings of a fox from that of a raccoon because the fox's has undigested feathers in it while the coon's has broken shells. The Fish and Wildlife people, who have the upper hand here, are declaring war on foxes [WORD ILLEGIBLE] "managed habitat" of 262 bird species - another migratory bottleneck and wintering ground as well.

Botany time: Hellickson explains that marsh older grows down to the high-tide line in the marsh. Salt meadow grass (Spartina patens), which farmers used to mow for hay, needs wetter earth. Where it stops, its cordgrass cousin takes over between high- and low-tide lines. Patches of Spartina alterniflora fall in high wind to create mattress-like mats of reeds. The fiddler crabs live below these, their million burrows ventilating the mud at low tide, irrigating it when the water returns twice each day.

There are phragmites too, hollow reeds that John Howard Benson once carved into pens to create America's finest classical calligraphy.

Salicornia, which adds zest to salads, thrives in the tidal water, its round spikes shiny from expelled salt. Snails creep up and down the flat grasses eating algae and keeping above the reach of the water whence their ancestors came and periwinkle cousins still teem. Seemingly sterile salt pans - flat areas of empty mud - are actually alive with different-colored algae that migrate up and down.

Sometime in June the marshes will be kept nearly people-free by mosquitos. Why not annihilate them? their larva is a prime food for the shell and finfish that spend their youth in shallow marsh waters. Without the eggs of these bloodsucking pests, three-fourths of the fish we eat might go hungry before growing up and going to sea. Raymond B. Manning, a Smithsonian zoologist, offers this datum: A recent year's catch of marsh-dependent seafood amounted to 535 pounds per acre of wetlands, perhaps twice what an acre of farmland can grow in livestock. (Half a million acres of wetlands have been filled or drained since the 1920s.)

Closer to the beach there's poison ivy, a plentiful source of berries for sixty bird species. Sea lavender and seashore goldenrod grow on the higher dunes. Hellickson says, "Terns used to nest here" on the beach near Tom's Cove where some vehicles are allowed. Their mating ritual, like the heron's, has a surprising initial object: for one individual to discover another's gender since both sexes look identical.

[WORDS ILLEGIBLE] drive south, [WORDS ILLEGIBLE] another guide. [WORDS ILLEGIBLE] Cheriton [WORDS ILLEGIBLE] two-foot [WORDS ILLEGIBLE] out of [LINE ILLEGIBLE] eighty per cent [WORDS ILLEGIBLE] shellfish has [WORDS ILLEGIBLE] markers [WORDS ILLEGIBLE] touch bottom a [WORDS ILLEGIBLE] of times before the [WORDS ILLEGIBLE] is done, though West knows these waters like the Carters know Plains. He has plied them, oysterman and boy, as his father and grandfather did. Now retired, he plans to ferry folks to the new Virginia Coast Preserve. But these bays are treacherous. Underwater shoals migrate like happy drunks in a singles bar. Creeks open and close before they're printed on any chart.

We're heading for the dozen barrier islands recently bought by the Nature Conservancy which will see that they're not tampered with in perpetuity: Metomkin, Cedar, Cobb and the rest. People are welcome to visit by day, so long as they don't disturb the plants or wildlife and take out everything they brought in. Rod Hennessey, the Conservancy's young man in Wachapreague, says the organization will leave these 35,000 acres of islands to their own devices as they shrink, grow, rotate and migrate, supporting gently balanced and well-studied ecosystems all the while.

Going outside into the edge of the Atlantic, the boat is surrounded by a pod of feeding porpoises. Minutes later West says, "I owned a thousand acrers right about here." The islands once lay farther east; the course he steers crosses land where his grandfather lived until the hurricane of '33. "All got in safe except my grandfather and old Mr. Cobb. We didn't know anything about hurricanes then, called them northeasters. Nobody could conceive a tide could come that high . . . Any man says he can build something the ocean won't tear up is overlooking a whole lot. He's a damn fool pure and simple. And that covers it all."

The entire coast may have once looked like these islands now: low, with broad beaches that slope gently to a short dune. When storm waves strike these shores, they waste their energy on the easy slopes. There are salt marshes and fresh marshes, some stands of loblolly pines on sheltered islands, whale bones, bird rookeries and, no doubt, more man-eating bugs than grains of sand when the summer wind is wrong. These islands seem so midest - unimposing and unimposed on.

Smith Island lies even with the tip of the Eastern Shore. (I rounded that point one hot afternoon, looking for timid oyster catchers. When thunderheads crossing the bay reached the narrow land, their forward edge began rolling up like sterile cotton out of its blue paper. A few huge drops fell like pints, it seemed. Then the rain blew horizontally, turned to hail as big as mothballs and was gone in an hour.) Now the peninsula road becomes the Bay Bridge tunnel leading to Norfolk and the summer metropolis, Virginia Beach.

Seaward motel towers offer views of Navy ships heading in. The sky is alive with jet fighters on training flights. The beach beyond the concrete promenade is covered with human young. A blad jogger puffs by. Four slim, blonde, coiffed young men sway in counterpoint like herons. A young couple in street shoes pushes a stroller along the hard wet sand. Two girls in electric bikinis flip a Frisbee. Hundreds of others lie face down, basking with their bra tops untied.

In a nearby office complex, incongruously, Dennis Holland fields phone calls about a pair of peregrine falcons, fastest birds on earth. The species is scarce but this pair is nesting on a bank building in downtown Norfolk and getting fat on pigeons. Holland is boss of the Back Bay Wildlife Refuge. The road there bends around small farms, reaches the water at Sandbridge and turns south again between summer homes on stilts high enough to look over the barrier dunes - if another house isn't in the way. They have names like Seaduce and Mermaison.

Romie Waterfield, who has worked at Back Bay for twenty-three of his fifty-eight years, explains: "My forefather was shipwrecked on the dune." The English sailor's great-great-grandson, born near the Refuge, remembers eating swan at a time when a man could shoot whatever he chose if he couldn't get a duck or goose. Now Waterfield tends the birds: "hell diver," the pied grebe which sinks to hide underwater, snowy egret - "when he jumps up look on his yellow dancing slippers"; "puddle ducks" that feed on the surface; "ditty birds," which include everything from song sparrows to mockingbirds, and 18,000 whistling swans that winter here.

"There are those that think ducks was created for hunters to shoot. It couldn't be farther from the truth." He points out there is a species with every length of neck to feed on every kind of aquatic plant in the marsh. While feeding, "he's tearing roots up, knocking seed off and covering it up. What he's doing is cultivating better than a man can. Other than that you wouldn't have nearly as good a crop of aquatics as you have" - to feed the birds.

He knows every bird he sees, and every plant: the bay tree, with a shiny leaf to flavor stew; juneberry; chokeberry; the evergreen wax myrtle tree with smaller fruit than the northern bayberry bush; a sumac which "makes the most delicious vinegar you every saw;" black cherry; red maple; live oak; cattail you can eat like cucumbers; and sea oats which hardly grow north of here.

He dislikes the refuge beach with its buggies of "people who don't want to know you," and occasional bare sunbathers whom he reports to the police. "I remember when the birds nested on this side of the dune," he says, driving a battered pickup along the beach. He hasn't seen that in years and doesn't know whether to blame the RV traffic. He does know this beach "used to have lots of birds and few cars. Now it has lots of cars and few birds." He steers slowly near a stranded gannet, feathers clotted with oil, sitting immobile just above the wash. It looks like a judge, its straight sharp beak pointed down, its frost-blue eyes unblinking. "There's nothing to be done," Waterfield says. He has found his first killkeer nest of the year near his house. The robin-sized bird rushed him first, all puffed up like a cartoon turkey, then fled, feigning a broken wing. The nest holds four speckled eggs.

Two hours south over winding back roads, the Cape Hatteras National Seashore begins. Veteran ranger Clay Gifford is proud that no species of plant or animal has left these islands since it became a park in 1953. He arrived seven years later but people still frequently bring him pieces of animals he's never seen before. (Sometimes he'd rather have a job "drawing the little boomerangs on Formica.") Eddies of the Gulf Stream sometimes launch flying fish near shore, and roll god-knows-what tropical things along the bottom. There are bottlenose dolphins "in numbers," grampuses, pilot whales, turtles, a few otters, even fewer shy water mocccasins, all sorts of crabs, bivalves and innumerable fish.

"You should have been here yesterday" was the early morning word south of Nags Head. The blues had been running; corpses of bait fish, each with a piece of flesh missing, clutter the beach in rotting proff. Light rain began an hour after dawn and most of the surfcasters went in for towels and breakfast. One young man stayed with his child, Shannon. Then, very quickly, the shallow surf is alive with shiny fish, perhaps six inches long, swimming in a tight-packed school to the edge of the wash. Then there are sloping fins among them: the tails of big blues at an orgy. They'd take one bite from a silver side and go for another. They take Shannon's father's lure too on almost every cast. He reels in, cuts the hook loose and runs down the beach to cast into the swarm again. Other fishermen must be watching from the porches like gulls for they're soon back sharing the prey.

The baitfish came in such tight schools that I could wade among them in the numbing water and slap a few ashore. The fishermen couldn't say what they were - menhaden, finger mullet? - or whether they were shoaling to spawn. "I don't know much about this," said Shannon's dad, "I just like to catch them."

Judging from caps and coveralls, most major corporations were represented on fishing piers: Exxon, caterpillar Tractors, even your Orking Man. Four buddies from Norfolk carted off eighty fish load by load in a little red wagon. Beach vehicles are popular here because "when the blues are running" fishermen can cast until the hunting school is gone, then drive a few miles ahead and fish again. So seventy broken miles of beach are rutted like a racetrack between the wet sand and dune line.

Marcia Lannon, "the littlest ranger" at about five feet flat and ninety pounds, works out of the former Coast Guard station by the Hatteras Lighthouse which was built 1000 yards from the surf and is now 100 yards away. In spring sea oats and beach grass are hard to tell apart, she admits, sharing her wealth of random comparative knowledge. Later the sea oats grow tall stalks with tattered flags of seed pods, which people like to carry home but mustn't lest they undermine the fragile dunes. The leaves of both plants curl in hot weather to conserve moisture. The two most numerous terns are easy to tell apart, once Lannon has compared them.

At the west end of Hatteras, ferries shuttle to Ocracoke and back, followed by swarms of raucous blackhead laughing gulls begging for food. This last island is completely dry (liquor-wise), the waitresses cool. The innkeepers turn away solos in case larger parties arrive on the last boat. But the water is warmer from the Gulf Stream and delightful swimming with a new-found beachcombing friend. It's sprintime still. The beach is empty except for an occasional jeep and the constant shorebirds.

Heading north finally, I realize J. Alfred Prufrock was wrong. "I shall wear white flannel trousers, and walk upon the beach./I have heard the mermaids singing, each to each./I do not think that they will sing to me." Of course not. Wool's crazy and he was looking for the critters in his head. Mermaids are only found on camper doormats and mirros behind condominium bars. There are better, real things to see and hear, choirs of gulls, ghost and hermit crabs, fastidious grasses, migrating clams in migrating sands and the ocean's endless energy.