Soon after Hurricane Sandy hit last fall, Joshua Harris, a billionaire hedge fund founder and an owner of the Philadelphia 76ers, began to fear that his $25 million home on the water here might fall victim to the next major storm. So he installed a costly defense against incoming waves: a shield of large metal plates on the beach, camouflaged by sand.
His neighbor, Mark Rachesky, another billionaire hedge fund founder, put up similar fortifications between his home and the surf. Chris Shumway, who closed his $8 billion hedge fund two years ago, trucked in boulders the size of Volkswagens.
Across a section of this wealthy town, some residents, accustomed to having their way in the business world, are now trying to hold back the ocean.
But the flurry of construction on beachfront residences since the hurricane is touching off bitter disputes over the environment, real estate and class.
Some local officials said they were worried that the owners were engaging in an arms race with nature, installing higher and higher barricades that could rapidly hasten erosion — essentially sacrificing public beaches to save private homes.
Last week, down the beach from Mr. Shumway's home, another project was under way. Bulldozers and backhoes were carting stones and piling sand, assembling what appeared to be ramparts. It was to protect the home owned by Vince Camuto, one of the founders of the Nine West fashion brand.
These fortifications have been built along a stretch of coast just over 2,000 feet long in one of the most exclusive sections of Southampton, off Gin Lane. The houses they protect cost as much as $60 million and stand, flanked by swimming pools and tennis courts, on hedge-lined lots of three to five acres.
Under local law, the beach in front of the dune is public, accessible to all. The section behind the dune belongs to the homeowners, but must be left open to the public. The homeowners are erecting the barricades on their parts of the beach.
Information about the projects was gleaned from interviews with local officials and zoning documents. Mr. Harris's alone cost nearly $50,000, according to town records. Others appear to have cost far more, interviews suggested.
The homeowners would not comment. Some of their representatives and consultants said the fortifications were environmentally sound and met all state and local regulations.
Still, the scope of the construction is dividing Southampton's full-time residents and its wealthy summer guests.
"If you lose the use of the beach, you've lost Southampton," said Fred Havemeyer, a member of the Town of Southampton board of trustees, which opposes the construction. "All these people are extremely rich and they're broadcasting the message of 'Me first.' "
Mr. Havemeyer and other trustees said the homeowners had taken advantage of a rule adopted by the State Department of Environmental Conservation after Hurricane Sandy that permitted damaged bulkheads and other beach fortifications to be rebuilt outside standard procedural requirements.
Some of the homes already had protective structures, but they were much smaller. The trustees have asked the conservation department to investigate whether the new structures violate existing restrictions.
The department said in a statement that it "continues to look into this matter."
Several of the protective barriers of boulders and bulkheads are now covered in mountains of sand so high that they obscure much of the houses when viewed from the beach.
Mark Epley, mayor of the Village of Southampton, acknowledged that officials had signed off on the projects, and that the homeowners might have a right to carry them out under current rules.
Still, he said, he grew so concerned after the barricades started going up that he took a building inspector to evaluate them in the middle of a nor'easter, "with sand smacking us in the face."
"When I first saw them, I was very taken back," Mayor Epley added. "It's alarming."
Anthony C. Pasca, a lawyer for Mr. Shumway, said the plan for the reconstructed stone barricade on the beach in front of Mr. Shumway's house was checked by officials from both the Village and the Town of Southampton. (The town includes the village.)
Village officials inspected the work after it was completed, confirming that it was done correctly, Mr. Pasca said.
The project "was meticulously planned, permitted by all levels of government and completed in accordance with those permits," he said in an e-mail.
Some defenders of the barricades said that with ocean waters creeping forward year by year, homeowners were unlikely to stand by and let their properties be washed away.
They recalled the fate of Westhampton Dunes, a beach community west of Southampton, where a failure to employ adequate protection led to the destruction of nearly 200 homes during severe storms in the 1980s and early 1990s.
"I don't think it's reasonable to point to every sea wall that exists and say it's a problem," said Aram Terchunian, a coastal geologist who has advised some of the Southampton homeowners on their beachfront defenses.
"You need all the tools in the toolbox in order to effectively deal with these erosion problems," Mr. Terchunian said. "And to ban them for philosophical and political purposes is shortsighted and certainly isn't scientific."
Robert Young, a coastal geologist hired by the Southampton trustees to evaluate these and other projects, said the beaches on Long Island were formed from sand carried from the eastern tip along westward currents. Sea walls seal off sand and sediment, preventing this drift, starving beaches farther west.
Mr. Young added that erosion became more pronounced at the edges of sea walls because water bends as it rushes off the wall face, carving out the sand on the sides.
"If you build a structure like that, the beach is going to disappear," he said. "The sea wall is not there to protect the beach. It is there to protect the property behind the beach."
He said several states, including the Carolinas, Oregon and Texas, had largely banned the use of such barricades.
New York has not, though they must be approved by government agencies, including the State Department of Environmental Conservation.
Mr. Havemeyer, the town trustee, recalled that he grew up on the beach here in a stately home owned by his grandmother. His mother sold the house in the 1960s because she believed that the ocean would one day wash it away.
That might well have occurred had subsequent owners not built their own bulkheads. Today, the house survives behind a metal shield, but the effects of trying to hold back the ocean are visible.
The house sits precariously on a promontory, the sand on all sides of the bulkhead washed away. Wooden stairs that once led onto the beach now dangle about five feet above the sand.
Mr. Havemeyer said there was only one solution to the threats from storms: "Pick the houses up and move them back."