On a foundation of special interest legislation approved three years ago, a large and politically powerful sand and gravel firm is seeking to build a processing plant that environmentalists contend could imperial Maryland's largest natural hardwood swamp.

The ordinance, which allows gravel washing facilities to be located as "special exceptions" in rural areas, sailed through the Prince George's County Council after the influential Bevard family's Silver Hill Sand & Gravel Co. was unable to obtain industrial zoning.

The 308-acre plant site, which adjoins land that is already being mined, lies near the headwaters of the Zekiah Swamp, at Potomac River tributary that runs for 20 miles through Charles County.

The local swamp is not as large or as well-known as the Everglades or the Okefenokee. Indeed, some people say it is not a swamp at all, but rather an intermittent stream gone haywire from man's futile efforts to drain and till its low-lying edges.

But the Zekiah, a 13,300-acre body of woodland and water, is highly rated by the Smithsonian as a fragile, ecological "jewel," a home for the rare Southern bald eagle, red-bellied woodpecker and Zekiah Stonefly, as well as for the more common diamond-backed terrapin, beaver, mink, heron and osprey.

The gravel plant, however, could by the ruination of the swamp, the county's staff planners say, and, nearby residents predict, the beginning of the "New Jerseyfication" of their rural area: a string of noisy, dusty, unsightly gravel plants and who knows what else.

The objections of both the professional government planners and the residents have so far been overruled. The winners -- the powerful Maryland sand and gravel industry, which annually mines some 12 million tons of stone worth $32 million.

And near the Zekiah's origins, just above the Prince George's County line, are some of the richest deposits of sand and gravel this side of the piedmont plateau.

"We are," said one Prince George's politician, proudly, "The gravel pit of metropolitan Washington."

So while gold and silver fever grip the rest of the nation, half a dozen mining companies dig feverishly for this lucrative local mineral in the Cedarville area 25 miles south of Washington. The raw material, however, must now be trucked for processing to plants located in heavily congested suburbs.

At the processing plants, water is used to rinse the raw material free of the clay and other impurities that are left to settle in a series of four rain-filled ponds. The ponds, which resemble resevoirs, are connected by pipes and are periodically dredged. Water from the last pond, which is the clearest, is pumped back to the washing plant for reuse.

On many occasions, Maryland Department of Natural Resources files show, ponds at the Bevard plants have overflowed, because of too much rain, clogged pipes, inadequate dredging or other causes.

The threat of similar spillovers affecting the Zekiah combined with the noise, dust and additional truck traffic that come with a gravel plant have brought together a loose coalition of nearby residents and outside environmentalists. The Sierra Club, the Chesapeake Bay Foundation, the Audubon Society, the Maryland Conservation Council have all objected to the proposed plant.

Charles County, too, has vehemently protested the facility, whose fate will next be decided by Prince George's County politicians.

The opponents suffered a setback last month when a zoning examiner's 60-page ruling dismissed most of their concerns as groundless. They are planning to appeal to the County Council, and the matter may ultimately wind up in the courts.

One of the most vocal opponents has been Elizabeth Schwien, a fiesty, 71-year-old widow who owns 185 acres next to the Bevard land. Years ago, her father and his team of horses helped build the first hard-surfaced road, from the crossroads known as T.B. to Leonardtown in St. Mary's County. She now lives along part of that road -- U.S. 301.

"I ain't against Bevard himself," she said recently during a tour of her Cedarville property. "He's just a gravel man and no worse than the rest of the world. It's just the nature of the beast. It's like a cowbird laying its eggs in the middle of another bird's nest.

"We weren't doing him any harm, and I guess he's entitled to his own crops, but, well, anyway, they're disturbing our life system or pattern or whatever you call it. To pick out a unique area like this and destroy it is the crime of all crimes."

The gravel plant site lies between two sections of the 3,500-acre Cedarville State Forest, which contains campsites and picnic areas. John Westerfield, the park superintendent, has told officials he's afraid noise from the plant will "spook the game and intrude upon the quiet enjoyment" of the forest by human visitors.

Westerfield is also worried that any break in the raised mounds of earth around the ponds would send silt across his parkland and into the state fish hatchery and fishing ponds nearby.

Says Stanwyn G. Shleter, a professional botanist for Scientists for Urban Wildlands, "why destory a unique natural area for all time for the benefit of a transitory sand and gravel operation?"

Up at the Bevard headquarters, Sam, Jr., 50, known, as Sonny; Marion, 41; John, 36, and several other members of this $16 million-a-year mom and pop business will tell you.

"It's a very basic industry," said Sonny. "Without sand and gravel, there can be no . . ."

"Houses, highways," Marion said.

"Glass," said John.

"No development at all without it," finished Sonny.

"Once you cover up gravel with a building, it's lost forever," added Frank (Bud) Bevard, a cousin. "It's a perishable resource. God isn't creating any more of these deposits. If you cover it, you never get it back." c

And the Cedarville deposits, Sonny said in their office filled with Lions plaques and baseball trophies, are "beautiful. Prime material."

Sam Bevard Sr., now in semiretirement, began the business in 1938 with one truck and a contract to supply road building materials in Southern Maryland. Now, it is known as Bevard Industries, a sand and gravel conglomerate with several corporations and 300 employes, including nine Bevards.

The main office is still in Marlow Heights, off St. Barnabas Road, where it has been since 1942. They mined the land there and under nearby Iverson Mall and Ourisman Chevrolet, which rose from the pits. "You just take off the tops of the hills," said Sonny.

They have had overflow problems here, they admit, because the gravel washing ponds sit in a valley sloping towards Henson Creek. "When it rains three inches here, hell, you might rise six inches," said Marion. "Down there," in Cedarville, where the land is flatter, "it's easier to control."

Locating a new washing plant where the travel is just sound economics, a transportation saving of 6 to 8 percent, the Bevards say. "To keep some control on our costs, we have to be as efficient as possible," said Marion. "The public ultimately pays for our costs."

The Bevards bought 610 acres near Cedarville in the early 1960s and have been mining parts of it since. Now, about 1,500 tons a day are removed by drag lines and front-end loaders and trucked to processing plants in Marlow Heights or Clinton, where another 2,000 tons a day are being mined.

In 1968, Bevard sought industrial zoning on the site, but the county planners balked at such a radical change for a rural area. Bevard then took a different tack: legislation to allow the plant as a special exception. Although still requiring official approval a special exception is presumed to be acceptable unless opponents can prove otherwise.

Marion Bevard is treasurer of the six-member Southern Maryland Natural Resources Association, which represents the sand and gravel industry, and his name heads a list of "resource persons" found in the County Council file on the bill.

The sponsor, council member Francis B. Francois, said the sand and gravel industry "probably supplied drafts" for the bill. What emerged, moreover, appeared tailor-made for the Bevard site, requiring at least 300 "contiguous" acres that could, however, be divided, as was the Cedarville land, by a power line or railroad tracks.

Before it passed, 4 to 0, the bill was amended to allow new washing plants in addition to relocated ones. Testifying for the bill were two politically connected attorneys representing Bevard and another company and a single conservationist who favored the ordinance.

"Sand and gravel operators should be encouraged to relocate their processing facilities to loss developed areas, perhaps even to locations where the natural materials are mined," said Bevard attorney Glenn T. Herrell Jr., without mentioning the Cedarville tract.

After the bill became law, Bevard withdrew the rezoning applications and applied in March 1978 for a special exception.

In June 1978, the county park and planning board recommended approval of the processing plant over staff objections. "If the risks were akin to national security such as a nuclear plant, or a missle installation, some compromise would be logical," the planning staff said.

"But a wet processing plant has importance only to the economic viability of the county, and to the private interests of its proponents," the staff said. "Once the Zekiah Swamp is damaged beyond recovery, it is gone -- and future generations will suffer its loss."

The planning officials did require Bevard to produce an environmental impact statement. Not surprisingly, the consultants Bevard hired concluded that only a very unlikely "catastrophic event" -- such as an earthquake, meteor or airplane wreck -- could cause the ponds to overflow into the two small tributaries running through the site and into the Zekiah.

Testimony heard during seven hearings in 1978 and 1979 filled 1,000 pages of transcript. Altogether, 80 persons entered appearances, the majority of them residents and environmentalists opposed to the plant. To dramatize their concern, neighbors held a motorcade from Cedarville to Brandywine and nature buffs hiked into the swamp.

Over the years, the Zekiah has harbored peaceful Indians hiding from warlike tribes to the north, Lincoln assassin John Wilkes Booth fleeing southward toward Virginia, and Prohibition-era moonshiners who brewed their rye whiskey in hidden stills. In Charles County. "It is almost all privately owned, by Edelens, Jamesons, Mudds and Bowlings, families who have owned it for 300 years.

William T. (Ted) Bowling, the retired postmaster of Bryantown, grew up fishing and trapping in the swamp, and he isn't quite sure what to make of the upstream gravel controversy.

Of some things, however, he is certain: "The worst thing that happened to the swamp was timber-cutting. It's not like it used to be.

Speaking from the oack of his wood shop he added, "I've lived here all my life, right on the Zekiah. "There's nothing mystical about the swamp. It's just a swamp."