The experience of Keystone Landfill, located 600 yards over the Carroll County border in Pennsylvania, underlines the fact that listing as a national Superfund cleanup site does not guarantee speedy government action. It's also an example of how public fears may be unnecessarily magnified by the mere listing of a dump on the list.

Keystone was placed on the Environmental Protection Agency's priority list in 1987 and closed in 1990, but pollution studies of properties around the toxic waste dump have yet to get under way.

Claims by two neighboring landowners that their ground water was contaminated by the privately owned landfill were dismissed earlier this year by a federal judge. But that was a private lawsuit. EPA is still negotiating a cleanup plan to be paid for by the landfill owners and 11 others cited as contributing polluters.

The landfill has been the target of criticism by neighbors for nearly 10 years. EPA found contamination in the landfill's ground water. But the first major investigation of off-site pollution by an EPA contractor won't start until this summer, at the earliest.

The comprehensive plans call for studying areas on all sides of the landfill, as far south as Humbert Schoolhouse Road in Carroll County. The engineering firm will sample surface water and sediments, test monitoring wells and residential wells for heavy metals and volatile organics, and look for possible effects on wildlife and wildlife habitat.

But EPA told the citizens task force monitoring the landfill activities that they could not lobby the agency for a neighborhood health effects study. Their public comments on the subject were heard when Pennsylvania health officials made an earlier health assessment of the area, EPA noted.

Residents around the Adams County landfill may feel they have been put off by the government one more time, given the languorous pace of official action at Keystone. Yet there is no marked evidence of abnormal health effects in the area. And any serious contamination of ground water outside the landfill has yet to be proven.

The EPA study of surrounding lands should be launched as soon as possible to determine the facts and directly address longstanding, still unconfirmed, fears of Keystone's neighbors.