A federal judge has wiped out the Interior Department's historic landmark designation for a bucolic section of Virginia countryside, possibly opening the way for massive strip mining operations there.

The ruling by U.S. District Judge Robert R. Merhige could encourage opponents of the department's more than 1,500 such sites to challange their historic status in the nation's courts.

The judge, sitting in Richmond, ordered the department to produce clearer standards for what constitutes a landmark and attacked the process it has used in the past as "vague and open-ended."

The decison also may ease the path for two companies that hold rights to strip mine on the 14,000-acre Green Springs area of Louisa County for vermiculite, a flaky mineral used as a soil conditioner, in thermal and electrical insulation and in cat litter. A civic group has waged a bitter fight for years to block the strip mining, claiming the mines would destroy an area rich in Civil War history and filled with prized 18th and 19th century homes.

In Monday's opinion, Merhige disputed the historical claims and said the public had failed to have "meaningful opportunity" to argue against historic designation of the Green Springs district, and that the Interior Department's guidelines provided "no limitations on the [Interior] secretary's discretion." The judge also canceled easements restricting development that the department had acquired for much of the area.

But an Interoir Department spokesman yesterday said the agency has already addressed many of Merhige's complaints.

Tentative rules for designating national landmarks were published last November for the first time in National Register, said Stanley Siegel, of the department's Heritage Conservation and Recreations Service, which handles landmark designations.

"We don't know wether the judge is aware of these rules," he said.

Interior and Justice department attorneys said they had no comment on the impact of the case because they had not yet read Merhige's opinion.

The ruling could help the two companies with mining rights to the Green Springs area because the historic designation could have forced them to undergo lenghty public hearings on the environmental impact of any project in that area.

A spokesman for the largest of the two firms, W.R. Grace Co., said it had no immediate plans to begin mining there."I don't think we're ready to go in there yet," said John Thurman, Grace's Washington representative. "I thought that was a reserve for the future."

But the company will take advantage of its mining rights later, if not sooner, says Mario Favorito, a company attourney based in Cambridge, Mass. "Grace is going to continue to be interested in developing that vermiculite deposit at some point," he said.

Virginia Vermiculite Co., which participated in the suit to erase Green Spring's historic designation, has been mining vermiculite for more than a year on three acres along the perimeter of the historic site.

The operation at present is "very very small," according to John Sansom, who directs its Green Springs mining.

Whatever the companies' plans, Rae Ely, head of the preservationist group opposed to the mining, vows that Green Springs will be preserved. "We're prepared to do whatever has to be done," she said.

Ely speaks for a small group of preservationists who want to preserve the rich agricultural land of Green Springs, with its 18th and 19th-century homes.

They are opposed by the majority of residents in the county, many of them less affluent, who see the mining operation as a major source of revenue for themselves and the county. The County Board of Supervisors helped bring the suit against the Interior Department.

The prodevelopment forces are largely longtime residents of Lousia County, while Ely's group consists of many wealthy outsiders who settled recently into the area's older homes.

"While the national significance of the district's historic qualities is disputed," Merhige wrote in his opinion, "the area does constitute a beautiful and remarkably well-preserved concentration of 18th and 19th-century buildings or architectural merit."