For Maryland's beachfront resort town of Ocean City, this year's villian was the fierce mid-October storm that buffeted the shoreline with 15-foot waves at a time when the tides were unusually high. The result: torn sidewalks, cracked foundations, and tens of thousands of tons of sand lost to the sea.

About 150 miles to the south, in Virginia Beach, the enemy has been the relentless easterly winds, which for more than two weeks have nibbled away at the beaches, endlessly pushing sand out to sea and bringing none of it back.

But underlying these seasonal setbacks is a more fundamental problem, a problem almost as old as the Atlantic coastline. All along the Eastern Seaboard, miles and miles of beach are gradually giving way to the sea.

Even though much of the sand pulled out to sea in the fall and winter comes back in on the gentle waves of spring and summer, "you never get everything back that you lose," explained Robert Henry, a geohydrologist with the Delaware state government's Department of Natural Resources.

The beaches are migrating upward, and the sea level is rising very slowly in relation to the land," Henry said. "Plus, the land is sinking slightly . . .

"The sand is being moved north along our coastline, and a lot of it is being lost every year," he added.

The trend has been going on for many centuries, Henry and other erosin experts say. But it is only in recent decades that man has intervened in the byplay between the beach and the sea.

As massive resort playgrounds grew up along the eastern beaches in the last hundred years, the sand has become an integral part of the economy.

On the one hand, it serves as a long, tantalizing playground, luring millions of summertime vacationers to the seaside. On the other hand, the sand is part of the ground on which their homes and condominiums are built.

"The problem comes when man wants to live close to the shore and builds structures where they can be attacked by the waves," said Andre Z. Szuwalski, the coordinator of the analysis section of the Costal Engineering Research Center in Virginia.

"It's because man is so close to the ocean - that to me is the major problem," Szuwalski added.

Over the years, Delaware's Richard Henry said, some small seaside towns in his state have had to literally pick up their buildings and move them back from the encroaching sea. Some spots along the coast lose three to nine feet of beach annually, he added.

Nonetheless, this fall's storms have been more dramatic than normal, breaking through some of the protective dunes that line the back of most Atlantic beaches. The Oct. 14 storm "washed right through the dunes in a couple of places," said Bill Schultz, an official of New Jersey's Department of Environmental Protection.

It also washed out a street in the southern New Jersey beachside town of Avalon, he added.

In Ocean City, the same storm undermined the ground-floor parking lot of the Oceana condominium, causing large holes to open up, and in one case leaving a Thunderbird suspended by its numpers 10 feet above the beach.

In the aftermath of the latest storms, which some observers called the worst in three years, there has been a concerted effort to quickly mend the damage in the hardest-hit spots.

The day after the storm, Ocean City's Mayor Harry Kelley ordered the first bulldozer out on his nine miles of beaches, pushing up the sand from just below the waterline, and piling up large man-made dunes in key spots.

However, as soon as the bulldozers nose out beyond the high tide line, they have trespassed in the territory of the Army Corps of Engineers, which has jurisdiction over the nation's navigable waterways.

The corps had agreed only to allow Mayor Kelley's bulldozers to shore up the hardest-hit spots; Kelley has defied them and, supported by Maryland's Department of Natural Resources, has kept nine bulldozers working along the full 130 ocean blocks.

In general, explained Szewalski, whose Coastal Engineering Research Center is a divison of the Corps of Engineers, when bulldozers are used to shore up a beach, "you're not adding any sand. You're just rearranging it on the beach face . . . it's not really a long-term solution."

What long-term solution would be best for the Atlantic coastal towns is a matter of often acrimonious debate.

David Ladd of the Corps of Engineers' Baltimore office speaks for most erosion experts when he says, "the best solution is to replenish what nature's taken waay" and either pump sand in from a mile or so offshore, or bring inland sand out to the beach.

But this can be expensive. In New Jersey a $20 million bond issue will be put before the state's voters on Tuesday, to finance 34 different public works projects, mostly in shoreline counties that are losing their beaches.

"It's a matter of defining policy," explained Delaware's Henry. "We want to help protect property on a short-term basis . . . over a period of time it could get very expensive.

"We're really trying to fight Mother Nature."