Several years ago, irritated by the condescension of District and lower Montgomery County residents, commuters from Gaithersburg launched an informal "upcounty and upfront about it" campaign.

The I-270 traffic, always bumper to bumper, was suddenly sticker-to-sticker with "I Gaithersburg" signs. Area realty companies opened upcounty offices to tout the low crime and relatively lavish spaces of the exurbs. The Marriott's gift shop discovered a hot property in its "Where the heck is Gaithersburg?" T-shirts, wearable road maps pointing to a star in the north.

But as the "new" Gaithersburg falls into the shadow of even newer high-tech high-rises, the joke may be turning around. With the opening tomorrow of the Shady Grove subway, those "Where is Gaithersburg?" T-shirts are beginning to look like nostalgia items.

"It isn't just that they spent the money to look old and established," mused a diner at Harvey's Restaurant on Shady Grove Road, the stolid, five-year-old clone of the 125-year-old downtown veteran. "It's that the way development is going, 10 years from now, this may not be here, either."

Subway construction has traditionally followed population paths, but with the Shady Grove station, Metro has emerged, in the words of local boosters and builders, as a "full partner in the process." (In fact, the subway's proximity to the many light and high-tech industries, which makes it as much of a convenience for outbound commuters as inbound, may throw a curve into the old traffic patterns.)

While at Bethesda and Rockville, the subway has inspired extensive renovation and redevelopment, the Shady Grove station has sparked millions of square feet of new construction -- barely the beginning, say county planners, who estimate the Gaithersburg vicinity will eventually be four times as crowded.

The subway's influence is so sweeping that county officials and developers often compare it to the transcontinental railroad -- a symbol of forcible civilization that lends dignity to the continual bulldozing of farmland. But there are many who mourn the wide-open spaces, who were hoping to keep a little country in the community.

"When we moved up here 15 years ago, it was because we wanted the children to have a back yard," said a State Department analyst who has put his Gaithersburg split-level up for sale. "But it loses its charm when the view of the fields gets filled up with other people's kitchens."

It doesn't take an archeologist to read evolutionary confusion in the Shady Grove neighborhood. A host of services and indulgences aimed at the new and newly affluent residents -- a saddlery, a suntanning spa, a fitness center, an abortion clinic and a couple of singles' bars -- look out at the interstate on one side and cornfields on the other.

The holiday traffic at Lakeforest Mall backs up to the deer hunters' trucks from Seneca. The county's huge solid waste transfer plant lies a half-mile from historically protected Washington Grove, chartered in 1874 as a Methodist Chautauqua town.

Nirvana lies to the west, but only for National Geographic Society employes: Lake Nirvana is just one of the man-made preserves (including lakes Placid, Elysium, Inspiration and Halcyon) off limits to the public.

Within this decade, as the Harvey's customer predicted, the face of Gaithersburg may change as drastically again. The Shady Grove station and the massive highway construction associated with it are at the heart of the Gaithersburg Master Plan, a blueprint for local development that makes the Bethesda facelift look like a paint job. Officials don't discuss the impact on the community; they talk about the effect on the region.

Although the master plan calls for development to be "staged" -- that is, coordinated with highway construction to make sure the already congested area doesn't choke -- county environmental protection director John Menke says residents "don't have any idea" what lies ahead.

"Even in Bethesda, you're talking only 30 percent more development," Menke said. "The master plan allows for 300 percent more development in the Shady Grove corridor."

"They don't have any idea," echoed Washington Grove activist Peggy Erickson. "I wonder how the owners of those nice new $150,000 homes are going to feel about having an interstate running through the front yard."

Erickson is scarcely exaggerating. When planners say casually that road construction is "heavily biased" toward the Shady Grove neighborhood, what they mean is that the Metro station is the terminus of at least 10 major highway projects -- one, the three-mile I-370, at a cost of $40 million per mile.

Several of these, such as the new Fields Road between I-270 and Rte. 355, the extended Research Boulevard and Gaither Road, and the first section of the Mid-County Highway between Rte. 124 and Shady Grove Road, have already cut through the cornfields. If longtime residents felt besieged before, they are surrounded now.

"I've lived within five miles of the same place all my life," said Paul Briggs, a 71-year-old farmer-handyman, shaking his head, "and I don't know where half these roads go. I can't even figure where they come from."

The upper suburbs of Montgomery County have long since ceased to be the cheaper alternative for young couples buying their first houses. Development companies such as Ryan Homes are pitching their subdivisions straight at the "new" upcounty commuters, who might be called the "uppie Yuppies."

"If you look at our ads for Park Overlook," said Bob Coursey, Maryland regional manager for Ryan Homes, "we're talking about 'the movers and shakers who don't have time to waste coming and going,' and we have a picture of two people standing at the Shady Grove station."

"When we look at a piece of ground, we're looking for marketability," Coursey continued. "We just opened a single-family development called Redland Ridge, which features a new line of designer homes that range from about $120,000 to $140,000. It's the first time we've offered those in Maryland, and we chose that location because of the prestige associated with the subway."

Ryan Homes alone has put more than 200 new houses near the Shady Grove station, and in the next two years Coursey said it expects to market 250 more. Hollybrook, the new Magruder Co. development on Crabbs Branch Road, includes more than 300 houses, mid-sized compared to plans for more than 700 units on the old National Golf Course site at Rte. 355 and Muddy Branch Road.

These and similar subdivision developments are often touted as the "upcounty explosion," but Menke, a former president of the county council, is wary that the boom may backfire.

"In the late '60s and early '70s," Menke said, "new homes were going up in the county at about 6,000 to 8,000 a year, which seemed a 'reasonable' level given the amount of services and schools and so on. It dropped off for awhile, and then stabilized around 4,000 to 6,000 a year.

"But for the past two years, new construction has averaged 12,000 homes a year. It's going to put tremendous pressure on local businesses. How do you gear up for a threefold increase in traffic?"

And in fact, housing development is only one aspect. By 1986, the commercial projects already under construction in the Shady Grove area will add nearly 3 million square feet and 8,500 jobs to the mix.

The unprecedented pace of development along the I-270 corridor over the last decade has transformed Gaithersburg from a community into something more like a medieval city-state -- a geographical coincidence of dozens of subdivisions and self-contained corporations. Montgomery Village, the 2,000-acre maxi-development, has nearly 25,000 residents in its various town house, apartment and single-family subsections.

Employes of the high-tech firms along I-270 (known as Biotech Alley, a jab at California's Silicon Valley) and the medical centers off Rte. 28 nearly equal that, but at a distance: Biotech Alley, it seems, is also a cultural gap. While the office buildings are concentrated on I-270 and its parallels (Research Boulevard, Piccard Drive), the housing developments, announced in a billboard frenzy at the interstate exits, sprawl around Quince Orchard to the west and Muncaster Mill Road to the east.

This split will have a pronounced effect on commuter traffic, especially as subway ridership increases. For area residents, the Shady Grove station will be the gateway to Washington: From there they'll head south to work or to the shopping and entertainment that Metro offers "only minutes away."

But for much of the other Gaithersburg population, the growing work force, Shady Grove will be the destination -- the Farecard to the timecard. This phenomenon, which has been increasingly apparent in the down- and midcounty areas, is called "reverse flow"; and many urban planners believe that intracounty commuters are the work force of the future.

"It's already a significant factor," according to Montgomery County transit services chief Ed Daniel. "It's the best-kept secret in the county, but along the Wisconsin Avenue-Old Georgetown corridor and down into Silver Spring, we have more [bus] riders going out in the morning than coming in" to the city.

"According to the 1980 census, there were 18,000 District residents working in Montgomery County," Daniel added. "A lot of those were going to Bethesda or NIH and Silver Spring, but now you'll see people coming up to the industrial areas from lower in the county, and even from Arlington and Alexandria."

If reverse-flow forecasters are correct, the Shady Grove station could have as great an effect on employment patterns as on transportation.

For many years, the Beltway has acted as an economic cell wall that divided the high concentration of unemployed District residents from the upper suburbs where new jobs were plentiful.

Faced with the difficulty of commuting from the south, I-270 corridor workers gradually concentrated to the north, commuting down from Germantown, Frederick County and even Baltimore. At Bechtel Corp., where a van pool system of 43 routes services the 2,200 Gaithersburg workers, the average round-trip commute is 60 miles.

But with the expansion of the subway, companies can recruit aggressively from all parts of the region. Putting public transportation into the pitch "will be a definite advantage," said Honor Keane of Gillette Co.'s employe benefits office. "We end up drawing only from Germantown or Rockville because the transportation is so poor."

"In fact, I mentioned it to a young woman we were interviewing down in the District the other day," said George Tucker, administrative manager for NCR. "It didn't affect her decision . . . . but it did give us a new angle."