So when erosion became a serious threat to bluff-top homes in the village of Siasconset on the island’s southeast shore and homeowners decided to fight back by replenishing the beach, cost was not an issue.

About two dozen of the owners joined with other island residents to form the Sconset Beach Preservation Fund, whose members are seeking permission to spend at least $25 million of their own money to dredge 2.6 million cubic yards of sand from a few miles offshore and pump it onto a 3.1-mile stretch of beach in Siasconset, or Sconset, as it is called here.

They realize that the sand will inevitably wash away, so they are prepared to do much of the work all over again, perhaps as often as every five years.

If the sand had to be transported by dump trucks, it could take 260,000 trips at 10 cubic yards a trip. Instead, it will be dredged up from the ocean bottom, mixed with water and pumped to shore as a slurry that will spew out onto the beach.

The goal “is to see that Sconset Village does not wash away,” said F. Helmut Weymar, a retired derivatives trader who lives most of the time in Princeton, N.J., but has owned a house on Baxter Road, the heart of the project area, since the 1970s.

“Were this only about our private property, would I have put this amount of time and resources into it?” Mr. Weymar said. “My answer to myself is no.”

His family’s house is in imminent danger, he said, but it would be “pretty simple” for them to buy another one.

It remains to be seen whether even endless expenditures can hold back the sea. There could hardly be a more difficult spot to protect than the southeast corner of Nantucket, a 47-square-mile “sand pile in the ocean,” as one owner calls it. The island lies about 30 miles south of Cape Cod, which offers some shelter to the island’s north shore. Cobble shoals to the east could, in theory, offer some protection to the island, but they perennially shift and some geologists believe they may actually be positioned now to funnel wave energy at the island’s vulnerable shore.

And because Nantucket — like Martha’s Vineyard, Block Island and Long Island — is little more than soil, rocks and pebbles left behind about 18,000 years ago at the end of the last ice age, it is easy prey to encroaching waves. The result is extreme erosion on the island’s south and east coasts, on average 10 feet or more per year, especially when storms roar in from the northeast.

More important for many here than the potentially enormous financial costs are the possible environmental costs of the plan, like threats to fish habitat. These are hot issues on all of America’s coasts, most of which suffer erosion expected to worsen as sea levels rise because of global warming.

On Nantucket, the issue is further complicated by history.

Some of the rose-covered weathered gray cottages of the Siasconset village center date to the 17th century — the National Park Service declared the entire island a historic district in 1966 — and their fate may be linked to the fate of the beach the fund supporters hope to replenish. The more recent but still decades-old influx of wealthy summer residents is also a complication.

“The language of class warfare creeps into it,” said Dirk Roggeveen, administrator of the Nantucket Conservation Commission, which has crucial permitting authority over the beach project and has yet to rule on it. “People concerned about the project make statements like ‘they are just rich people trying to protect their houses.’ ”

The fund’s permit application is in effect an assessment of virtually every economic or environmental impact that could possibly occur, and a description of how the group would avoid, monitor, mitigate or compensate for it. For example, fishermen objected that the sand washing off the newly built beach would scatter their prey, so the proponents offered to compensate them for reduced catches. And when conservation commissioners and others said the problem was not just loss of fishing income but the stirred-up sand’s degradation of offshore fish habitat, project backers offered to create an artificial substitute.

Much more than the beach in front of supporters’ homes would be rebuilt; the project would run from north of Sankaty Lighthouse, already scheduled to be moved from the bluff edge, to a town sewage facility on the south side of Sconset village.

A northeaster in April cost some homes on Baxter Road as much as 20 feet of land. And recently, iron beams and other equipment had been assembled on the front lawn of one of these houses in preparation for moving it to the very edge of the road, a task that will cost tens of thousands of dollars, at least, and will buy the owners perhaps one or two more April-strength storms.

Other Baxter Road property owners have already moved their houses to the edge of the road, or across the street to land they owned or bought there. Others are planning to move, even if it means shrinking their building footprints on their diminished lots.

The current attempt to save the beach is hardly the first effort to protect the houses that line the bluff at Sconset. In 1994, the property owners began an ambitious test of a new beach preservation technology, called “dewatering.” They installed a network of pipes to drain water out of the beach, in theory making it less vulnerable to erosion. Instead, the project itself was largely washed away. A sandbag operation, ostensibly more benign than the dewatering, has been going on for years.

Robert Colletti, who works for Holgate Partners, which operates a sand pit on Nantucket, stood recently in the back of the house on Baxter Road that is about to be moved. It now sits only about 15 feet from the bluff edge. About 100 feet below him, at the bottom of the bluff, workers were filling giant jute fiber bags with sand and arranging them in a kind of terrace, in hopes of preserving what little of the bluff remains between the house and the water. The hopes may be slim.

“The North Atlantic,” Mr. Colletti said, “it has no mercy.”