Scott Fosler yesterday became the first Montgomery County councilman to break ranks with the council on the issue of the controversial Laytonsville landfill, as he agreed with its neighbors that a liner is necessary to guard against groundwater contamination.

In a memorandum to County Executive Charles W. Gilchrist and his council colleagues, Fosler said that a liner and a cap "would provide an added measure of security" for the Laytonsville residents.

Previously, the council has questioned, but agreed with, recommendations by state health officials that a liner is not necessary.

Members of the Greater Laytonsville Civic Association, who recently hired a New York firm to show that the design of the 550-acre landfill is unsafe, lauded Fosler's proposal, but said he did not go far enough.

The current design of the landfill calls for a system, preferred by state officials, that would allow the natural cleansing processes of the soil beneath the waste to filter out contaminants. Officials of the Maryland Department of Health and Mental Hygiene argue that a liner could crack, causing contaminants to concentrate at the fault line.

Fosler said that his decision was only partially influenced by the Laytonsville citizens and a report from the New York firm that supported the liner concept.

It was unclear yesterday how Fosler's proposal would be received, but another council member, Rose Crenca, said, "Psychologically, we have done enough damage to that neighborhood," Crenca said. "If putting in a liner is safe, then that is what we ought to do."