The Montgomery County Council approved legislation yesterday designed to preserve farm land from suburban development without financially punishing farm owners.

Described by Council President Scott Fosler as "the most significant thing the council may do in its four-year term," the legislation changes the zoning of farm land, which accounts for 40 percent of the county's area. The minimum size for a building lot in agricultural areas of the county will be changed from five to 25 acres.

To compensate farmers for the money they could have earned by selling their land to developers, the plan is designed to give them a certain amount of money, estimated at about $8,000, for each five acres of farmland they own beyond the first five acres.

The money will come indirectly from developers, who will contribute it to a new bank set up by the county in return for county permission to build projects at greater density than would ordinarily be permitted in certain non-farm-land areas of the county.

According to the plan, instead of selling land, farmers will sell developers "development rigths." The farmers' farm land is known as a "transfer area" and the land where developers build at a density greater than zoned is known as a "receiving area."

Critics of the plan, who include a few farmers, point out that the county has only one "receiving area" -- in Olney -- where developers can build at a greater density than zoned after buying "development rights" from farmers.

The council expects to approve other "receiving areas" when it votes on the new master plans for various regions in the county. The council expects to approve nine of the county's more than 20 master plans during the next two years.

Other opponents of the plan include developers and residents of the southern part of the county, who say they are afraid that density will be increased in their neighborhoods. County Council member Rose Crenca was the only member who voted against the plan, saying that it would have "an adverse impact on the need for housing in the county." Council members Elizabeth Scull and Esther Gelman were not present.

The plan was designed by the planning staff of the Maryland-National Capital Park and Planning Commission. Royce Hanson, commission chairman, told the council the plan was "significant not only for this county but for this country. There are severe problems in preserving farm land and this plan may give jurisdictions in other areas the courage to develop a plan similar to ours. This plan will make us remembered more for what we've preserved than for what we changed."