In a black file box in Ken Lowe's office here is the evidence of a real estate boom -- the names of 500 Washington area buyers seeking houses in Shepherdstown and Jefferson County.

Right now Lowe can't help them. There just aren't enough properties to meet the demand. The West Virginia panhandle, once a sleepy backwater, is fast becoming Washington's newest bedroom suburb.

Lured by extraordinarily low taxes, cheaper real estate, breathtaking scenery and a commuter railroad that connects "the best of both worlds," Washington commuters have moved the metropolitan fringe to a new frontier. Jefferson County 60 miles northwest of Washington has grown more in the last decade than in the previous 120 years, making it the fastest-growing county in the state.

"We wanted a rural atmosphere, near the railroad," said Clarence (Clancy) Kefauver, chairman of the board of Columbia Federal Savings & Loan Association in downtown Washington and, for six years now, a panhandle commuter. Kefauver's rustic home here in Shepherdstown commands a sweeping view of the meandering Potomac River, and he and his wife, Dorothy, say they do not miss their Bethesda lifestyle a bit.

"I used to live six miles outside Washington near I-95, and it took at least an hour to get to work driving and I used to be a wreck," said Nancy McDermott, a Capitol Hill stenographer who moved to a mountain home near Harpers Ferry four years ago and now relaxes on the commuter train.

The newcomers' presence is palpable in the early morning and evening hours, when cars clog the country roads and turn the train parking lot at Harpers Ferry into a New Yorker magazine cover of Westchester commuters scurrying to make the 7:15.

On any weekday, there are from 150 to 200 cars in the depot parking lot.

"When I began commuting 10 years ago, if you got 12 cars down there, it was unusual," said Bill Gavin, a former Bethesda resident and Xerox employe who trains downtown three times a week to hustle convention business for the Cliffside Motor Inn at Harpers Ferry.

The Washington comuter boom also has begun to change the political and cultural complexion of Jefferson County: The politics of Shepherdstown, a college community long before the commuters came, now are largely dominated by ex-Washingtonians, who also own Georgetown-type restaurants and shops. Countywide, natives still hold all the elected offices but Republican newcomers have created at least the potential for two-party politics in a county completely dominated by Democrats since the Civil War.

With the influx of outsiders have come scattered subdivisions and "Lots for Sale" signs over much of the county. The newcomers also have sparked stormy debates over lack of zoning and basic services of government that are taken for granted in the D.C. area but are alien to this region.

"These people come up here from Montgomery and Fairfax because of the low tax rate, and they immediately demand all the services they had down there," complains Henry M. Snyder Jr., president of the county commissioners. "We don't have any free lunch here, any more than they did where they came from."

Despite the 47 percent growth spurt of the 1970s -- from 21,280 to 30,300 people -- Jefferson County still is small enough to get by with a single high school and, many natives feel, minimal government. But if the trend continues unabated, many natives and newcomers alike fear, the special rural qualities that both groups enjoy could disappear. Current projections anticipate 45,000 residents by 1995.

Jim Louthan, a dairy farmer here, has seen it happen before. He was born and raised on a farm in Rockville, and 20 years ago his family fled an earlier suburban advance for the rich rolling countryside just beyond the Blue Ridge that is known hereabouts as "The Great Limestone Valley."

"It's a matter of seeing it happen the second time," he said in the kitchen at his 500-acre farm. "There is plenty of land in this county that can be developed without hurting the agricultural industry. Unfortunately, agricultural land is the easiest and cheapest to develop."

Louthan is one of a growing group of farmers who have signed voluntary five-year agreements not to sell their land to developers. In return, the county has promised to eschew "nuisance laws" such as telling farmers when they can run their grain driers. The agreements, which are recorded at the county courthouse in Charles Town, are part of an effort to head off what Louthan refers to as "the impermanence syndrome," a state of mind that by accepting change contributes to it.

Like a majority of natives, Louthan opposed county-wide zoning, which was soundly defeated in a 1976 referendum. It is, he admits, a dilemma.

"You know we can't stop progress," said Bill Henshaw, the seventh generation of his family to farm the West Virginia panhandle, "but we gotta have some control. How we're gonna do it I don't know because in this society of ours the government shouldn't dictate what you do with your property."

Henshaw reluctantly supports zoning. Most of the support for such controls has come, however, from the newcomers. Foremost among them is Robert L. Beckett Jr., a transplanted Marylander who is the county's controversial planning director.

Beckett, who was hired in 1973 to administer a newly-adopted subdivision law and to prepare the zoning ordinance that was rejected by a nearly 3-to-1 margin, is viewed by critics as antigrowth and as "a voice in the wilderness," according to one developer. His aim, he insists, is only to moderate the growth, not stop it.

Beckett's beliefs have brought him into conflict with commuters at times. He is all for mass transportation and energy conservation but worries that a new commuter parking lot at a virtually unused railroad crossing called Duffields could be a "growth magnet" in the area. Negotiations for the lot are proceding anyway.

What makes life possible for many newcomers to West Virginia is, of course, the train. Actually, there are three of them stopping at Harpers Ferry, for which commuters gladly pay $91 a month. It is literally their lifeline. And, it seems, it is threatened almost constantly.

Terry Flaherty, the gregarious president of Friends of the Railroad, has been commuting by train to Washington for a decade. Now in charge of all auto parking for Senate employes, Democrat Flaherty is more worried about losing his train than his job, now that the Republicans have a Senate majority.

West Virginia's powerful politicians who are about to be dethroned include Sens. Robert Byrd, the Democratic majority leader and head of the Transportion Appropriations subcommittee, and Jennings Randolph, Environment and Public Works Committee chairman, and Rep. Harley O. Staggers, who chairs the House Interstate and Foreign Commerce Committee and did not run for reelection. All, Flaherty points out, were strong supporters of commuter rail service from the panhandle.

"Everybody's anxiously awaiting the appointment of a good secretary of Transportation," Flaherty said.

While the trains carry an estimated 600 commuters a day, an untold number drive the distance over an expanding network of superhighways to jobs in the close-in suburbs. They do it despite the high cost of gasoline that would seem to discourage such travel.

Cecil Arnold, for one, drives to Arlington, where he is a police investigator. His wife, Pam, takes her car to Great Falls, where she runs a gourmet kitchen shop.

"We both feel it's worth the commute," she said, from her home in Willowdale, an exclusive subdivision "offering superior sites for homes of "distinction" just outside Shepherdstown.

But paradise has a price tag, at Willowdale and subdivisions like it throughout Jefferson County. Typically, homeowners pay $125 a year for road maintenance and $36 annually for trash pickup. In some subdivisions, they pay for security as well. Since the services are private, they aren't deductible. f

Still, the financial incentives are considerable. Gavin, the Harpers Ferry motel operator, estimates his taxes are 30 percent what they were in Montgomery County. Retired military men get an extra tax break from the state. To ease the pain of high interest rates, banks currently are offering Jefferson County-backed mortgage money at 10.35 percent, far below market, for those earning up to $40,000.

What Jefferson County gets in return is a matter of some dispute. The county has little industry to keep its workers at home, and limited shopping to attract their dollars. "Unfortunately," said farmer Bill Henshaw, "people moving out from the city don't contribute a whole lot. They don't buy here because there aren't a lot of stores. It's known as a bedroom community."

From one such community, however, came a dissenting view. Susan Hough, a Charles Town native, now lives in Security Hills, a subdivision teeming with unleashed watchdogs. Hough's husband, also a native, drives to work as a forklift mechanic in Gaithersburg. Their neighbor across the street works in a Rockville nursery. He came from Maryland and she does not know his name.

The impersonality of suburban living and the subdivision sameness that at least some newcomers came here to escape does not threaten Susan Hough.

I think growth's fantastic," she said from the front door of her new split-level. "For a long time, there was nothing. I just like to see my home town grow."