When Christy Carton moved from Arlington to this farming community in Frederick County seven years ago, she never counted on becoming an expert in industrial pollution, she said.

Today, a whole room of her house is filled with files, all about the plant several miles north operated by Eastalco, the county's largest private employer. The company's aluminium-smelting plant processes unrefined ore into the shiny metal used in everything from pots and pans to tennis rackets and jet aircraft. Carton and her neighbors believe it is polluting the county.

Residents have complained, without much success, about the threat of wastes produced by the plant, particularly contamination of well water with the cyanide they say is leaching out of disposed materials.

Now, on the eve of a legal showdown over the issue, their concerns may be resolved in an out-of-court settlement that their lawyers say could have implications elsewhere in the country.

Carton's civic association, another local group and the Environmental Defense Fund filed suit two months ago in U.S. District Court in Washington, charging that the federal Environmental Protection Agency failed to meet a congressionally mandated deadline for determining whether certain mining and smelting wastes were hazardous.

As part of its smelting process, Eastalco uses hundreds of brick "pot liners" that become laced with flouride and cyanide residues, which must later be disposed of.

The pot liners are some of the industrial wastes under study by the EPA.

The government must respond to the suit by Dec. 10, but lawyers for both sides said this week they hope to reach a settlement that will avoid a full-blown trial.

A spokesman for Eastalco, which does not figure directly in the case, declined to comment about the suit or on allegations about pollution at the site.

But Carton, one of the leaders in the citizen's campaign, said she is hopeful that the suit will provide a long-awaited breakthrough in the local fight against alleged pollution from the plant.

If the plant's smelting byproduct is declared hazardous, it would have to be disposed of under the Resource Conservation and Recovery Act, a federal law setting forth strict regulations for the handling of hazardous industrial wastes, lawyers for the citizens said.

"The impact of the case will be much broader than Eastalco," said lawyer Michael S. Elder, who represents the plaintiffs. "We're dealing with an issue that has national significance in regard to wastes generated by the mining industry."

EPA once considered the bricks hazardous, but a 1980 amendment to the act exempted so-called "mining wastes" from the EPA's list of hazardous substances, until their actual danger could be studied.

The amendment was only supposed to cover the huge piles of spoil produced during an actual mining operation, according to Sen. Jennings Randolph (D-W.Va.), a member of the Senate Enviromental and Public Works Committee.

But a lobbying effort, led primarily by smelters, convinced EPA that "mining waste" included materials produced during the smelting process, said Penny Hansen, chief of EPA's waste treatment section.

In 1981, after receiving no public comment to the contrary, EPA pulled pot liners off its list, pending completion of the study, Hansen said. The study was supposed to be finished last year, but is now scheduled for completion in 1985.

As a result of that action, Carton said Eastalco terminated an agreement to recycle the pot liners through a York, Pa., firm and instead decided to bury them on its 2,000-acre plant site here. The company received a landfill permit from the state last year, but a consultant's study released in April found cyanide in groundwater at the plant site, Carton said.

The finding prompted the suit, which charged that a lapse in regulation by the EPA led to the contamination. Most residents get their water from wells, Carton said.

"I think it's a shame that the EPA has let the situation drag on unattended until citizens have to go to court to force them to do something they already should have done," Elder said.

The State Department of Health and Mental Hygiene, which regulates industrial waste disposal, has found evidence of cyanide contamination in groundwater here within the past year, and has asked the company to drill seven new test wells, in addition to 12 that are being used to monitor the site, said the department's John Lawther.