FREDERICK, MD. -- At the Gladhill Tractor Mart near the Frederick County fairgrounds, sales of large farm machinery are down, and owner Maurice Gladhill worries that the future of farming here could be bleak.

But a few blocks away, business is brisk at a Jaguar dealership where real estate brokers, builders and developers are buying the sleek British luxury cars priced at $42,000 and up.

A downtown building that used to house an old-fashioned hardware store is set to open as a sushi restaurant.

Stretching from Pennsylvania to Virginia 45 miles northwest of Washington, Frederick County, long Maryland's agricultural heartland, is dramatically growing and changing, shedding its rural, hayseed image and becoming a bedroom community with an upscale county seat -- Frederick city -- planted smack in the middle of it all.

While this new growth has brought a larger tax base and brand new shopping centers, it also has resulted in traffic jams, less farmland, skyrocketing school enrollments and gentrification of working-class neighborhoods that threatens the homes of some of the city's poor.

The state's largest county is still predominantly rural, offering panoramas of farms and mountains. But increasingly the landscape is dotted with scenes more familiar to urban dwellers.

The once slow-paced county seat, where farmers regularly came on weekends to shop, is now touted by some shopkeepers as "Georgetown North," complete with trendy restaurants, boutiques and antique shops in renovated buildings.

Fourteen years ago when Mayor Ronald Young took office, Frederick was "more a working-class town than now," Young said. "We have moved more toward the professional or white-collar type of city."

The county's lower taxes and still relatively affordable housing have attracted thousands of amilies from the closer-in Washington suburbs who are willing to trade a longer commute for the amenities of a larger, detached house on a more spacious countryside lot.

But just as low-income residents worry about the effects of faster growth on their neighborhoods, the new suburbanites moving to the county fear added growth could rob them of the life style that brought them here.

"If you came in and built on one acre and kept it somewhat country, I wouldn't object," said Gary (Skip) Moore, a WTTG (Channel 5) technical director who grew up in Wheaton and moved a dozen years ago to a subdivision a few miles over the line from Montgomery County.

But the way things are going, Moore fears, "it'll be just like Wheaton, just like Montgomery County all over again."

It is almost programmed to happen in some sections, under the county's 1984 master plan, which targets growth for farmland surrounding the county seat and in areas closer to Montgomery County.

At one end of what its boosters called the "Golden Triangle" formed by I-95, I-70 and I-270, Frederick has moved into the metropolitan mainstream. As the Washington area moves west into the fertile foothills of Appalachia, the state's leading dairy county is losing its uniqueness.

From Middletown to Green Valley, from Buckeystown to Burkittsville and around Walkersville and Woodsboro, former farm communities are newly peopled by commuters, and fields that once sprouted corn now yield houses.

Lured by subdivisions beguilingly named Tranquility, Loch Haven and Picnic Woods Estates, the transplants do not yet vote in large numbers in local elections, politicians say, but their presence is still palpable, for example, in the school enrollment explosion.

In the county seat, the newcomers' presence is measured mostly in renovations and escalating real estate prices. In the city's historic district, property values have skyrocketed 25 to 30 percent a year, the mayor said.

The gentrification of Frederick, city and county, also has inflated rents to the point where some families have had to move one county west, into the Hagerstown area, to find affordable housing.

One small black community feels particularly vulnerable to change. Young said the city has made a special effort to preserve the neighborhood at its south end from market forces, by buying and reselling three homes to residents and subsidizing the renovation of 12 other units in return for 15 years of lower rents.

But at West All Saints and Ice streets, a short block from the Market Street renaissance, black residents remain fearful.

"They're trying to close Saints down, get rid of the blacks," said Arthur Hicks, 37, sitting on a stoop with his friend Weedon Bowie, 44. "There are a lot of people buying a lot of stuff trying to move the blacks out who were born and raised on this street."

Elsewhere in the county, growth has brought metropolitan-style rush-hour traffic up and down I-270 and its tributaries. A commuting trip to Bethesda or Silver Spring that took an hour 10 years ago "would now take almost two hours," said Skip Moore's wife Theresa, a 1967 graduate of Silver Spring's Einstein High School.

Betty Floyd, a Frederick city alderman who moved here from New Jersey 22 years ago, said her husband took 2 1/2 hours to drive home one recent Friday from his Army Department job 57 miles away in Alexandria.

"I see Fairfax with its terrible congestion problems and northern Montgomery County with its congestion problems," she said. "I'd hate to see that happen to Frederick County. I'm very concerned."

Among others watching the area's growth with a wary eye are farmers. The city is aggressively annexing farmland to broaden its tax base, and in return, the landowner becomes eligible for city water and sewer service and the property becomes more marketable to developers.

The dilemma gripping the farmers of Frederick is that they have no intention of developing the land themselves but cannot afford a retirement fund apart from the equity in their land.

John and Elizabeth Crum are lifelong farmers who have watched the city creep north toward the brick farmhouse they built in 1940.

The Crums say the city asked them to seek annexation, and they were hard put to say no. So 113 acres of their 400-acre farm are to be included within the Frederick corporate limits. But both say they oppose more development.

"Not as long as I'm living do I want it developed," said Elizabeth Crum. "I don't like what I've got beside me. Three or four times a day, people are calling saying they heard our farm was for sale. I'm sick of it."

As further evidence of its stronger link to the national capital region, the county recently joined the Metropolitan Washington Council of Governments and is now considered a part of the Washington standard metropolitan statistical area.

The COG membership gives Frederick a say in matters affecting the mushrooming Washington region. But behind this move, which county commissioners long resisted, is an array of telling statistics: The population of the City of Frederick increased 25 percent to 35,004 in half a dozen years. County population is up 18.4 percent since 1980 to 135,960, ranking it among the fastest growing in the state. Countywide, a record 2,100 home building permits were issued last year, 400 more than in the previous year. In the current rezoning cycle, the county commissioners are to consider the most applications in the county's history. After a 900-student enrollment increase this past year, the school population is expected to grow by 1,000 in September. This record growth already is crowding classrooms and straining education budgets.

Along with newcomers who have flocked to subdivisions in Frederick, businesses, too, have moved up the corridor from Washington's suburbs.

British Auto Services, the local Jaguar dealer, moved here from Rockville.

County boosters and politicians express delight over the recent arrival of Washington and Baltimore developers building office parks. The Marriott Corp.'s computer data center is scheduled to move from Bethesda to the new Frederick Business Center.

Last week, however, the county's Economic Development Commission drew the line at two quarries proposed for an area south of Frederick city as "inconsistent with the tone, theme and nature of development encouraged" for the county.

In the city itself, there are plans for the type of development officials prefer. Snaking through the south side of town is Carroll Creek, which regularly overflowed before a new flood control project. Now, Young said, he aims to turn it into the third-largest attraction in Maryland, after Ocean City and Baltimore's Harborplace. To study the possibilities, he recently led a city delegation to San Antonio's Riverwalk, which has shade trees, boutiques and restaurants.

While the Carroll Creek version remains to be seen, Frederick's west end is a booming strip of new shopping centers known here as "the Golden Mile."

Near the heart of Frederick's historic district, Harry Schildt, 79, sat on his steps under an awning chewing a cigar. A retired barber, he said he doesn't like the changes that have hit his home town. The preservationists even tried to get him to take down his awning, he said. "They're going to extremes a lot," he said.

But despite his complaints, Schildt said that he at least has a tenant for his basement barbershop: a shop that features clothes from an earlier era.