In the unceasing battle over Huntley Meadows Park, environmentalists have fired their weightiest salvo yet: a 3-inch-thick volume filled with reasons why the proposed Lockheed-Van Dorn Connector would cause irreparable harm to the 1,262-acre nature preserve.

The study, prepared by a panel of scientists on behalf of the Citizens Alliance to Save Huntley Meadows (CASH), contends that Fairfax County officials have failed to consider adequately the effect of the road on environmentally sensitive wetlands in the park.

In July, the county released plans to build the road with an elaborate system of pipes, bridges and ponds that officials said would actually expand, rather than destroy, wetland areas.

The CASH study termed the county's plan "fatally flawed" and called for a full-fledged environmental impact statement.

"The county has understated drastically the size of the wetlands within the park, their relationship to a large chain of vitally important wetlands outside of the park, and the unique nature of Huntley Meadows as a wildlife habitat and as one of the increasingly rare places for the public to experience the values of inland wetlands," the study said.

Fairfax County Board Chairman John F. Herrity said this week that the county government will have no comment on the study.

The $13 million road was conceived in 1968 and would provide a direct link between Rte. 1 and the Springfield Mall area of Fairfax, diverting thousands of motorists a day from a network of inadequate neighborhood streets.

But the 2.2-mile road would traverse the northern section of Huntley Meadows, one of the region's largest park and wetland areas and home to more than 200 species of birds, including the bald eagle. The Interior Department will make the final decision on whether the road can be built.

Manus J. Fish, the regional director of the National Park Service, which is part of Interior, said this week that he had read the document in its entirety. "I think they bring out some good comments," he said.

But he added that a timetable for a decision has not been established. The county hopes to begin construction in 1989.

The CASH study draws on the expertise of dozens of scientists and environmental groups, including the Sierra Club. According to the study, the county's treatment of the issues is "rife with manifest errors, contradictions, uncertainties, and ambiguities . . . . "

While the study addresses such issues as noise, traffic and air pollution, its principal concern is wetlands.

Joan Darling, a biologist whose comments appear in the study, said the county's plans to create ditches and ponds would disrupt the normal ebb and flow of the wetlands and "decidedly change the nature of the flora and fauna of the area."