The eastern end of Long Island may be better known for its swank Hampton resorts, Peconic Bay oysters, and its inexhaustible supply of ducks, but it's about to take the nation's lead in a field of great significance to housing and the environment.

The county government here plans to begin paying off farmers next week - to the tune of $50 to $55 million by next year - to keep on farming, rather than selling their acreage to subdivision developers.

In the first program of its kindever undertaken on a large scale by a U.S. locality, Suffolk County will buy the development rights to an initial 3,800 acres of potato farmaland in several locations, But not buy the land itself.

It will pay farmers the estimated difference between what they could obtain from sale of the acreage to home builders and what it's worth as farmland.

In general, the "difference" is estimated to be a whopping 80 per would gladly pay $5,000 an acre brings only $1,000 an acre for agricultural usage.

The program - originated by county executive John V.N. Klein as the only way to stop suburban sprawl while still treating landowners fairly - already is a model for other jurisdictions around the country.

Maryland's Howard County and jurisdictions in New Jersey, Pennsylvania and Massachusetts are studying Suffolk's approach or drafting their own versions.

And it has received support at the federal level from at least one congressman - Rep. James M. Jeffords (R-Vt.) - who has introduced legislation authorizing $50 million a year in matching grants for communities preserving farmlands via purchase of development rights.

Klein hopes to expand the program to 12,000-15,000 additional acres out of the county's 56,000 remaining farmland acres by carefully choosing lots directly in the path of development.

Klein insists farmland preservation "is not antidevelopment" or anti-housing, but rather is a method of exerting permanent controls on where tract subdivisions are built.

Suffolk County, he argues, holds attractions to New Yorkers and out-of-staters who swarm to its becaches, bays and Hamptons because it is semi-rural, dotted with duck and truck farms, relatively untouched by bulldozers.

If Suffolk looked like Nassau County, 80 miles to the west at New York City's doorstep, nobody would make the trip. Yet the economics of land development in recent years - plus the existence of high speed transportation to the city and its employment environs - brought the building boom to Suffolk's potato patches.

The preservation program works like this: A farmer (or agricultural land owner/investor) who agrees to participate conveys the rights to any further usage other than farming of his property to the county, in an amendment to the recorded deed. He then receives compensation - at whatever figure he negotiated, based on appraisals of the property's worth - and still holds title to the land.

He is now roughly 80 per cent as rich as he would been by selling out to a developer, and is free to do whatever he wants on the property, provided it is agricultural. He can even sell the land, subject of course to the deed's prohibition of development by subsequent owners ad infinitum.

The farmer gets to do what he'd like to do - keep on farming but be able to afford to drive something better than a jalopy - and the county achieves its purpose, which is to limit growth in key areas.

"Farmland preservation" is an important new wrinkle on the environmental horizon, and can be expected to be tried in dozens of metropolitan areas - including Washington - in the coming years.

But as Klein readily admits, supporters will need both fund-raising ability - $50 million out of a county treasury is no small potatoes - and political fortitude, commodities not always in long supply.