Maryland's top health official said yesterday his department probably would approve installation of an impervious liner beneath the Laytonsville landfill, which is to open next month, but such a liner isn't necessary to prevent groundwater contamination.

The landfill, on a 550-acre site near the town of Laytonsville in Montgomery County, has been bitterly opposed by residents of the area, who hired a consulting firm that produced a report saying the design of the facility is unsafe and a liner necessary.

In a letter to County Executive Charles W. Gilchrist yesterday, Charles S. Buck Jr., secretary of health and mental hygiene, wrote that "while the department would probably approve the installation of a liner at this site, it would not constitute the primary, nor even a necessary, protective mechanism." The landfill's designers contend the soil beneath the landfill will leach out any contaminants and that well water in the area will not be affected.

Buck's letter and an accompanying report were in response to a request by Gilchrist for a review of the project and any health risks. The idea of lining at least part of the landfill with clay or another impervious material has been endorsed by County Council member Scott Fosler. Fosler also favors placing a cap over the first part of the landfill to open, a step backed by Gilchrist.

Buck endorsed the idea of capping the first 100 acres to be used at the facility. He was critical of the consultant hired by the Laytonsville residents, saying that the firm's conclusions were not based on new data and did not demonstrate that the county and state were in error in planning for the landfill.