Wearing quilted jackets, string ties and suspenders, the dairy farmers who sat in a Frederick County courtroom last week are not anyone's image of political activists. But they are part of a new group of environmentalists: those who claim that industrial pollution damages their livelihoods as well as the quality of their lives.

The dairy farmers, are suing an aluminum smelter, Eastalco, for $4.8 million, charging that fluoride gas emissions from the processing plant - located near their forms in southern Frederick County - have harmed their dairy cattle, reduced milk production, and damaged trees and crops on their farms.

The farmers and ranchers who have become caught up in environmental fights in Maryland, Virginia and across the nation are not "any kind of nutty fruit and feathers people," one federal official noted. They are taking environmental battles to court for a simple and compelling reason - economic self-interest.

"It's a very interesting trend - different people looking to enforce environmental law for different reasons," said Joan Z. Bernstein, chief counsel to the Environmental Protection Agency. "It's not because they're do-gooders, but people who have been harmed."

In Western Maryland and West Virginia, Christmas tree plantation owners sued a power plant and a paper mill for pollution-related damages to trees, winning one case, losing one and reaching settlements in others. Along the border between Virginia and North Carolina, farmers were part of a coliation that prevented the proposed dammning of the New River for a hydroelectric project.

In Michigan, the Michigan Chemical Co. and Michigan Farm Bureau Service has paid almost $40 million to settle nearly 700 claims airising from the 1973 contamination of cattle feed with a toxic fire retardant, PBB (polybrominated biphenyl). In Fernwood, Wash., cattlemen sued the Intalco Aluminum Corporation, a sister company to the Eastalco plant in Frederick, winning three lawsuits and settling 16 others.

In addition to filing damage suits against industrial firms, farmers and ranchers also have been involved in environmental issues in other ways. For instance, the National Farmers Union, the National Farmers Organization, the Grange, the National Association of Corn Growers and the National Association of Wheat Growers all studied strip mining legislation to make sure it included some protection for agricultural lands.

But it is by filing suits for damages that farmers and ranchers appear to play a particularly effective role in environmental battles.

"Whenever you have private enforcement of public rights it always results in an increase in control," said Bernstein. "Vulnerability to large-scale liability makes people behave in a certain way - mainly, very carefully."

"There are clearly some very interesting coalition types of interests emerging," said David Weiman, a former lobbyist for the National Farmers Union, who researches agricultural issues. Weiman and representatives of the Environmental Policy Center, which has worked with farmers and ranchers on environmental issues, predicted more cooperation between agriculturalists and environmentalists.

"A lot of people are always asking us - is the environmental community as strong as it was?" said Environmental Policy Center director Louise Dunlap, adding, "labels are less important. What's happening is more and more economic interests are getting involved in environmental issues."

During its opening week, the trial in Frederick has been replete with references to other groups of farmers and ranchers challenging other industrial interest either by opposing industry attempts to locate in farming communities or by filing lawsuits for damages.

It also has become clear during the trial that something of a small legal industry has grown up around these types of cases, just as malpractice cases have produced specialists in that area. A plant pathologist who testified referred to his previous testimony elsewhere around the country in similar suits.

The attorneys representing the farmers are from a Portland, Ore., law firm that also represented cattle men suing the Washington firm. Both the botanist who served as an expert witness and attorneys for Eastalco were involved in the Western Maryland Christmas tree plantation litigation.

Eastalco began efforts to locate in Frederick County near Buckeystown in 1967, and opened its plant in 1970, despite some citizen opposition. The smelter occupies 350 acres of a 1,900-acre tract, part of which is farmed by the corporation.

"Practically every year Eastalco leads the county in corn yield per acre," the company's attorney Benjamin Rosenberg said at the outset of the trial.

Eastalco chose Frederick County as a location for a variety of reasons, including its nearness to the port of Baltimore and to a relatively low-priced source of electricity, according to testimony. Aluminum processing is an energy-intensive process that consumes huge amounts of electricity.

The firm which employs 1,025 workers in Federick County, is a subsidiary of a French corporation, Pechiney Ugine Kuhlmann Group (which attorneys for the farmers characterized as the French equivalent of Alcoa) and Alumax Inc. The Frederick smelter produces about 175,000 tons of aluminum a year.

The three farm families - Charles and Lois Noffsinger, Austin and Norma Putman Sr. and their son and daughter-in-law, and William H. Zimmerman and his son - operate dairy farms bordering the smelter.

They are dairy farmers, part of the Capitol Milk Producers Cooperative that provides milk for distribution through the High's dairy stores. Zimmerman, the son of a German immigrant, was born and grew up in Frederick County and has been farming at his present location since 1947. With his son, he operates about 400 acres.

The farmers claim that flouride emissions have damaged the teeth and joints of their cattle, reduced milk production and made the cattle more vulnerable to disease. They also blame flouride emissions for damages to trees on their properties.

The first week of testimony involved various expert witnesses called by the farmers who testified to what they said were the effects of emissions from the aluminum processing plant on the farmers' cattle and properties. During cross-examination, attorneys for Eastalco have tried to cast doubt on the witnesses' expertise.

The trial is expected to last another two to four weeks.