Howard County would preserve 2,000 acres of rural land and decrease by about 1,500 the number of residences built in its western region over the next 20 years under a zoning plan released yesterday.

The proposal by county planning officials seeks to reduce allowable building on land zoned "rural conservation" from one residence per 4.25 acres to one per 10 acres. The plan also would eliminate the practice of allowing owners of rural conservation land to accept transfers of development rights from other areas, which often result in the building of one home per three acres.

Owners of rural conservation property, however, would have an incentive to sell their development rights on large parcels at one residence per three acres rather than building under the more restrictive one per 10 acres.

Also, 100 housing units annually allotted to the western region gradually would shift to the county's east and be earmarked for affordable housing.

Under current zoning, "we're giving up really good farmland," Marsha S. McLaughlin, director of the Department of Planning and Zoning, said yesterday. "We're trying to tip the balance so what we get is the best land being preserved."

The zoning proposal, the topic of a series of community meetings this summer, is drawing fire from builders and developers who say it is devaluing some of the county's choicest property. Howard officials want the Planning Board to conduct a hearing on the proposal within the next two months, then have the County Council review and act on the measure in the fall.

"We are fulfilling our commitment to farmers" who already sold development rights on their land, McLaughlin said. "We have an obligation to the farmers to minimize new subdivisions."

Howard officials have endured years of criticism about their agricultural land preservation efforts from state officials, who have pushed for down-zoning land in the western region to make it less attractive for building. The county has 19,200 acres under agricultural easements, but it has been unable to add land in recent years because developers have been offering $40,000 an acre for development rights, and the county can offer only about $20,000 an acre. State officials have said they may decertify the county's preservation program next spring if Howard doesn't do more to protect farmland.

The county's proposal, however, targets the "sweet spot of the region" that is often the setting for million-dollar-plus single-family homes, said Tom Ballentine, director of government affairs for the Home Builders Association of Maryland. "Some people are losing a good bit of equity under this proposal."

Steven K. Breeden, a principal in Security Development Corp. of Ellicott City, noted that lots in the region today are worth $200,000. Reducing the available lots by 1,500 means a loss of $300 million, he said.

"Who's losing it now?" he asked. "It is the landowners. It's the farmers they're supposed to be helping."