The amount of farmland in Montgomery County continues its historic decline, according to federal figures released yesterday, despite a tough agricultural preservation program long considered a national model.

Since the early 1980s, nearly one-third of the county -- about 140 square miles -- has been designated an "agricultural reserve" where tight limits on home building are intended to protect land for crops and livestock.

The Census of Agriculture figures released yesterday, however, show that the inventory of farmland dipped from about 124 square miles in 1997 to about 117 square miles in 2002. Twenty years before, about 166 square miles were farmland.

"We're continuing to lose farm acres," said Jeremy Criss, agricultural services manager for the county. "To think that we are going to stop that trend is not realistic."

Other counties in the Washington area have enacted similar regulations, designed to protect agricultural land from home builders. But these efforts in Montgomery and elsewhere have come under increasing attack by critics who see them as doomed exercises in rural nostalgia -- or worse.

Setting aside acreage for crops restricts the supply of land for homes, drives up housing prices and, in effect, excludes the poor, critics have said, citing several economists.

Whether the preservation efforts can succeed in permanently saving farming is also in dispute. Yesterday's figures offer some support to both sides.

Although the acreage farmed decreased, for example, annual sales of county agricultural products grew from $32 million to $42 million from 1997 to 2002 -- in inflation-adjusted dollars -- according to the census. The number of full-time farm operators also increased, from 237 to 291.

"The 2002 Census confirms that the agricultural industry in Montgomery County is alive and well," County Executive Douglas M. Duncan (D) said in a statement. "Montgomery County leads the nation in farmland preservation."

Yet such progress has come by diverting the program from one of its original goals: to conserve farmland so that the county had ready sources of food and fiber nearby. Toward that end, officials imposed restrictions to limit developers in the agricultural reserve to no more than one home for every 25 acres.

But Montgomery's agricultural vitality appears to have less to do with food production than it does with changes in what officially constitutes farming. Profitable nursery and greenhouse operations, along with farms that provide hay for horse owners in the prosperous county, are making up more of the agricultural reserve, according to yesterday's figures and interviews. In recent years, the county has sought to make it easier to set up horticultural operations and riding stables in the agricultural reserve, officials said.

"There's been a shift away from traditional farming to horses and horticulture," said County Council President Steven A. Silverman (D-At Large). "It doesn't mean that we are abandoning agriculture. It means we are expanding the definition of agriculture."

Making farming in Montgomery County profitable is considered fundamental to such efforts. But that has proved difficult.

In recent years, as the affluence of the region and housing pressures have risen, some home builders have been willing to pay as much as $200,000 or more for a buildable lot. Such prices provide an incentive for farmers to chip off a slice of their acreage to make extra money. But as they do so, the area for farming becomes fragmented.

"Everything has a price," said Drew Stabler, 66, who farms 1,500 acres in the agricultural reserve with corn, soybeans and wheat. "The question for farmers is: How long do you want to resist?"

It's not just farmers who want to sell, however, who are looking askance at agricultural preservation efforts.

Increasingly, planners and economists have grown more skeptical of such plans, of which Montgomery's might be just one of the most prominent. In recent years, Loudoun and Prince William counties also have imposed restrictions at least partly intended to preserve farming, and "smart growth" measures in many Maryland counties were intended to do the same.

"Protecting farmland just for protecting farms is just another form of NIMBY," said Gerrit Knaap, executive director of the National Center for Smart Growth Research at the University of Maryland. "It sounds like heresy, but the problem with food in this country is not too little, it's too much."

Economists have argued, too, that such regulations might provide residents with open space and a sense of rural character but also drive up the cost of housing.

"Regulated land use designed to increase the quality of life does have costs," said Susan M. Wachter, a professor at the Wharton School of Business and an assistant secretary at the Department of Housing and Urban Development during the Clinton administration. In 1990, she co-authored a paper on the effect of Montgomery's land-use policies on home values. "It increases housing prices. It's simply a matter of supply and demand."

As a result, the future of the agricultural reserve -- long a cornerstone in the county's planning and beloved by some for its "u-pick" orchards and country scenery -- is not clear.

"We're not interested in paving over every square inch [in] Montgomery County," Silverman said. But "there will be tremendous pressure for us to encroach on the ag reserve."

"There's been a shift away from traditional farming to horses and horticulture," said County Council President Steven A. Silverman (D).