W. Lambert Cissel, gunning the engine of his hulking farm tractor, joined 27 other tractor-riding farmers tonight in a parade outside the offices of the Howard County government to protest what they see as a "land grab" that would lead to the ruin of some farmers.

What has aroused their anger is a sweeping proposal to "downzone" 56,445 acres of prime farmland in a move designed to create an agricultural preserve that would be off bounds to developers in this fast-growing county 24 miles north of Washington.

Although the measure is supposed to protect farmers from the pressures of development, many at tonight's protest said that its restrictions would ruin them if it is adopted by the County Council.

"If this goes through, we feel it's going to make some of us go bankrupt," said Cissel, 47, a county native who grows soybeans and barley on a 500-acre farm in western Howard County.

The County Council, meeting as the Zoning Board, held the first of three scheduled public hearings on the proposal tonight as part of a broad review of land-use planning in the county that has been underway for several months.

Council Chairman Vernon Gray and council member Ruth Keeton, who had proposed the measure, declined to comment, citing zoning board rules that prohibit members from discussing zoning actions.

Both, however, seemed surprised by the size and intensity of protest.

"This is very frustrating," Keeton said. "I can't go into it any further than that."

Currently about 100,000 acres west of Rte. 108, which bisects the county, is rural, agricultural land. Under current zoning, houses there must be built on lots at least three acres in size.

Under the proposal, 56,445 acres of the choicest farmland would be placed in a new zone that would limit construction of houses to 20-acre lots and, in some cases, 30-acre lots, depending on the size of the farm. Opponents of the measure say that it would lower the value of the land, which now sells for about $5,000 an acre.

"A farmer works his whole life for his farm. If you devalue the land, he can't borrow money on it to buy seed," said Cissel. "We're afraid some of the banks will call our loans in if the property is devalued."

Many farmers also said they want to be able to subdivide their land to build homes for their children, but that assembling 20-acre lots would be too expensive and would take too much land out of production.

"The farmers are very afraid and very angry right now. It's really a big fight, and we have to win it," Cissel said.