Citizens battling a new county landfill scheduled to open in June in the Laytonsville area of Montgomery County unveiled a consultant's report yesterday that concludes that, as currently designed, the facility presents a "very substantial risk" to the public health and environment.

The landfill, which has been under construction since 1979, is scheduled to open as soon as the state permit for the county's current landfill in Rockville expires in June. Ray Schoenke, a former Washington Redskin who heads the Greater Laytonsville Civic Association, said the citizens concede it is too late to stop the landfill, but they want safeguards.

The $20,000 study, conducted by Fred C. Hart Associates, said that without a clay liner and a collection system to catch leaching chemicals, "irreparable harm . . . is likely to occur" from the landfill in the form of contaminating the well water that serves the surrounding community.

At a press conference yesterday, Steffan W. Plehn, a vice president of the Hart firm and formerly head of the U.S. Environmental Protection Agency's office of solid waste, challenged the county's assertions that the 550-acre site, formerly a farm called The Oaks, was the best of several considered.

Ed Rovner, special assistant to County Executive Charles W. Gilchrist, said the county had not yet seen the study but would "look at it and give it whatever consideration it warrants." Rovner said the state has informed the county that the artificial clay liner the citizens want would create, rather than abate, a hazard. "The state said an artifical design would be detrimental."

The county's own study found that the chemicals would not seep through the ground and poison the underground streams from which well water is drawn.

But the Hart study, Plehn said, showed a potential for groundwater contamination greater than that projected by the county. Plehn said contamination "can extend more widely" because of fractures in rocks under streams and "water withdrawal through wells beyond the area."

Already, Plehn pointed out, testing of monitoring wells around the landfill have shown increased levels of oil and grease, possibly from spills during construction of the facility.

The liner and leachate collection system the citizens say are essential could cost as much as

4 million. "That's what it's coming down to," Schoenke said. "It's a question of money versus people's health. The citizens are scared to death."

The Oaks landfill has become a potential political issue for this year's county elections. Schoenke and others say they are considering running for office, and a political action committee known as the People for Responsive Government has grown out of the antilandfill lobby, which has pledged to oppose County Executive Gilchrist's reelection.