Equipped with heaters and lights, the bulldozers are rolling around the clock along the nine miles of Ocean City beaches. Backwards into the surf, then out again, they crawl in a zig-zag pattern to rebuild the resort's eroded strand.

The winter has brutalized the beach where millions of vacationers flock each summer. Ten northeasters, some with 15-foot waves and excessively high tides, have pounded Ocean City since October.

In some places, the beach has nearly disappeared, leaving only a thin spit of sand between cottages and motels and the water's edge. In other sections, the beach is more like the typically narrow winter coastline, but it is disheveled into erratic bluffs and drifts.

Beach erosion is a persistent problem up and down the Eastern Seaboard. Severe winter storms this year have washed out sand from beneath beach houses on pilings on Fenwick Island and Bethany Beach, Del. In parts of New Jersey, the U.S. Army Corps of Engineers is considering emergency beach-fill operations.

Annually since 1974, deteriorating portions of Virginia Beach have been widened by hauling in sand dredged from a nearby Chesapeake Bay channel, and a $35 million project has been proposed by the Corps of Engineers to refurbish the entire resort coastline.

Because of progressive erosion in Miami Beach, some of the 9.3 miles of shoreline have completely disappeared. A corps sand pumping program under consideration would in some places more than double the present beach width at a 10-year cost of $64 million.

"It's really a battle, man's battle against the sea," said coastla engineer John Murphy of the corps' Philadelphia district.

Beach erosion is the natural result of numerous environmental forces, such as storms, slowly rising sea levels, the impact of inlets and shifting sands. In some areas, such as northeastern Florida, beaches wiped out by hurricanes have completely rebuilt themselves. On the Gulf Coast, geologists have charted a 16-year beach "life cycle" of sand erosion and accertion.

Beach contours change daily. In summer, gentle southerly winds drift sand onto the shore and build it up. In winter, northerly and westerly storm winds in conjunction with the natural southerly flow of sand along the East Coast cut away the beach and primary dunes.

Storms have the most severe impact on erosion because higher than normal tides and increased wave action pull sand from the beach. Even though beach sand naturally builds up again after storms from off-shore bars, the net result is still a loss of sand.

In the case of "barrier" beaches - those strips of land surrounded by water like Ocean City, Assateague Island and the Outer Banks of North Carolina - the problem is compounded by what scientists call the beaches' westward "migration" over generations.

The barrier island "doesn't actually march westward," said Turbit Slaughter, a Maryland Geologic Survey geologist, "but it recedes in that direction primaryly after storms."

The causes of this westward movement are storm winds and a continuing rise in sea level (six inces in the Chesapeake Bay since 1934) that washes the sand westward by waves and high tides.

According to geologic maps, the nine miles of Ocean City coastline moved westward an average of two feet a year between 1849 and 1942. Since then, despite many severe storms, the shoreline has stayed in approximately the same position. Slaughter's studies at certain points along the Ocean City coast since 1971 show that in those locations "the beach has maintained itself."

In addition, the sand has actually built up in some points. Along the southernmost 10 blocks of town the effect of a sand-collecting jetty in the Ocean City inlet has caused the beach to expand 800 feet eastward since 1933, he said.

For 22 years, however, that jetty has deprived the nothern five miles of Assateague Island to the south. Maximum erosion along that stretch was as much as 60 feet annually until 1965. Geologic studies after 1968 have found this beach also is now "maintaining itself," according to Slaughter.

This has been one of those unpredictable winters. Not since March 1962 when a northeaster hovered over Ocean City for three days, has the beach been so ravaged. After the 1962 storm, the Corps of Engineers constructed a stabilizing buffer dune along the beach to function with several sturdy timber sand-collecting jetties that the state began building there in the 1930s.

Whether this latest unusual amount of sand erosion is temporary or whether the sand will eventually be restored by nature's own cycle is not something local officials are willing to wait for. The livelihood of this town of 3,500 year-a-around residents depends on the appearance of an attractive shoreline.

The bulldozers are Mayor Harry Kelley's weapon in this war. A weathered stocky, self-proclaimed "red-neck" with sea-blue eyes and a crooked grin, Kelley has protected his resort like a southern sheriff.

A fighter by nature, he has feuded with every invading outside force form condominium developers to drug pushers - and he frequently wins. This time, Kelley has taken on the most guileless and relentless foe of all - the weather.

"There's nothing prettier in my mind than beach and that ocean, for fishin' or goin' into or comin' out of," he said. "I got a great love for this city - I put 'her' in the female. And that beach is our bread and butter."

Kelly called up his bulldozers as a quick and visible solution to his disrupted beach, something that would make investors, local businessmen, condominium owners and tourists feel secure about Ocean City. In the summer, resort business swells the town to 300,000 visitors each weekend and pumps $130 million into Ocean City's economy.

At low tide, the nine bulldozers push sand from the surf inland into rows like giant anthills 12 feet tall and 80 feet wide. Where the "bullies" have been, there is no flat beach, except at low tide. There, enormous sandpiles drop off abruptly six or eight feet above the surf.

When the "bullies" are finished, probably early next month, the sand will be tapered toward the breakers, so that vacationers will be able to enjoy the 100-foot-wide sloping beach that generally graces the coastline in summer.

Even then, lamented the mayor, "we can't get that beach back completely."

Two years ago when Kelley first applied for a bulldozing permit, the Corps of Engineers - which regulates coastal dredging - questions its usefulness as a first-aid measure with no known lasting effects and sought information about potential impact on marine life.

Although it could find no "overriding environmental consequences," the state Department of Natural Resources warned that possible damage to the surf clam, mole crab and other microscopic organisms in the bulldozed area could lead to "ultimate" damage to larger marine life that feed on these creatures.

"There was nothin' to substantiate statements that we were messin' with the ecosystem," Kelley contended. "Let's say for purposes of argument we were. What's more important, this life and property or those little mole crabsz".

Without a dredging permit, Kelley ordered his bulldozers to work last October, while leaning on his political popularity in Maryland for support. As he did other publicity that remainds tourists around the nation of Ocean City's existence, the mayor bled the new-making opportunities for all they were worth.

On Feb. 2, 1978, the corps relented and issued a two-year bulldozing permit. "Frankly, it was the political issue that turned it around," said Thomea Croyle, chief of the Eastern Shore permits section for the Corps of Engineers in Baltimore.

"In Florida, a form of bulldozing was tried on Jupiter Island but it was later discarded as an unsatisfatory solution. "All you're doing is temporarily moving a little sand around," engineer Hobbs said.

The state of North Carolina has had a number of requests for bulldozing permits this year, but the Corps of Engineers is attempting to discourage any large-scale authorization along the Outer Banks.

"You're robbing Peter to pay Paul," said Lim Vallianos, a coastal engineer in Wilmington, N.C. "There's only a finite amount of sand. If you start drawing from that, it's like drawing from a bank account."

There also is reason to believe that bulldozing can stimulate more shore erosion, he said. "The natural beach is the sum total of all the natural forces in the area. If you lower the beach strand, the waves do nothing more than attempt to rebuild it to its previous state to create a dynamic equilibrium along the shore line."

The corp's preferred solution, the offshore sand pumping and dredging, has been fought by Kelley as too expensive for his community. Bulldozing will coast about $400,000 this year, including $200,000 from the state and $50,000 from Worcester County.

However, the mayor has indicated that if the federal government will agree to finance 90 percent of the corps' beach restoration proposal and ease up on other local liabilities he might consent to the project.

In current figures, the sand pumping would cost $22 million initially and another $500,000 each year in maintenance. The new beach would have an average width of 190 feet, which in some places such as 14th Street, would be five times the present width. A 16-foot dune would also be constructed. If approved, the beach resortation is not likely to start until the 1980s.