In the gathering morning heat, three yellow Caterpillar tractors, their treads pulverizing the red dirt, crawled up a knoll and into a clearing in the heart of Fairfax County.

It's a scene repeated dozens of times in the Washington area every day, one more stand of trees being cleared for a gleaming office building. But on this site between I-66 and Lee Highway, the growing hillocks of earth, the deepening furrows and the felled trees mark a milestone that thousands of Northern Virginians will remember for decades.

The Vienna Metrorail station is scheduled to open tomorrow, and its coming has touched off a flurry of construction near the terminal that, by the time the dust settles, will change neighborhoods and the way their residents live.

"Vienna can't remain a small town when it's within 500 yards of a Metro station," said Camille Karim, 49, whose tidy brick house overlooks the station. "It's going to change drastically."

Because it is the last stop on the Orange Line, and because it sits on the median strip of I-66 near several other major roads and not far from Tysons Corner, Fairfax City and Fair Oaks Mall, county officials years ago singled out the Vienna station as a prime hub for extensive development.

Neighbors fear that in addition to altering the landscape of the county's midsection, the station's presence may sweep away the lingering small-town vestiges treasured by residents of the Town of Vienna (pop. 15,600).

Residents cite several things that set Vienna apart: The town's Halloween parade; a police force that can respond to any disturbance in town within two to three minutes; the July 4 celebration; and the Vienna Inn on Maple Avenue, where proprietor Mike Abraham serves up 80-cent chili dogs to an adoring clientele often crammed four deep around the bar.

"A lot of us have worked for years to help further the kind of atmosphere we have in the town of Vienna," said Martha Pruett, 67, a citizen activist who has opposed dense development near the station. "It makes me sick to think that buildings even eight stories would be erected there."

After nearly two years of dissonance, the Fairfax County Board of Supervisors, which oversees development in the area, voted last month to keep the current development restrictions in the area, rejecting heavy commercial building plans that had been proposed. The levels of residential development allowed in the current county master plan, however, are substantial, and many residents fear that the board may reverse itself after next year's elections and allow more commercial development.

The bulldozers that began crisscrossing the 57-acre patch of land near the station last week are preparing the site for six 12-story office buildings with a third as much space as the Pentagon, three six-story apartment buildings and 4,300 parking spaces.

That project, being developed by the Evans Co. in McLean, is just one of a half-dozen major projects planned for the area. A 61-acre tract owned by the firm of John T. (Til) Hazel, a prominent Fairfax developer, could be the site of several 19-story apartment buildings -- or, if Hazel has his way, office towers.

The county board recently rejected his plan for office and hotel buildings on the site, but the residential development is allowed.

The full impact of all the development that will spring up around the station is still a matter of guesswork for planners and homeowners; so is the full impact of local traffic that inevitably will accompany the new buildings. Planners predict that commuters will come to the new station not just from the neighborhood, but from western Fairfax County and the outer suburban counties of Prince William and Loudoun.

Karim, an American citizen who was born in Lebanon, lives east of the station just outside the Vienna town limits but considers himself a resident. He sells religious books for a living and spends his free time restoring a blue 1951 Packard sedan.

First as a renter, now as a homeowner, Karim has lived with his wife Ellen and their five children in the Town and Country Estates neighborhood for nine years. Seated on a white metal chair in the shade of a gnarled maple tree in his front yard, he spoke of his reservations about Metrorail.

Neither he nor his wife will have much use for it, he said, because neither has a job that requires travel into Washington. When Metro opens, and the projects around the station are completed, traffic on the local roads will only get worse. Already, he said, the cars heading to the Pan Am shopping center at the bottom of Nutley Street on Lee Highway are backed up a half mile in the afternoon rush hour.

They are concerned that the increased local traffic -- and the strangers it will bring to the neighborhood -- will mean his family may have to change some of its habits.

"We keep our doors open, our bicycles and kids' toys outside, and nobody takes anything," said Ellen Karim. "Little by little, it's going to change."

Said Manuel A. Odria, 32, a chauffeur who lives down the street with his mother: "In the back of your mind you're kind of afraid that all the care you take with your home will be for nothing. You think that eventually the place'll be a parking lot."

Odria and Karim's community is one of several distinct neighborhoods near the station, which is just south of the Vienna town line and more than than a mile from Maple Avenue, the town's bustling main street.

Close to the station, on either side of I-66, hundreds of families live in rows of pastel-colored and handsome brick town houses and generally well-tended suburban homes in a handful of neighborhoods with names like Country Creek, Five Oaks, Circlewoods and Briarwood.

Those names, dreamed up after World War II by developers who were building not suburban communities but outposts in what was then a residential frontier, suggest a woodsy setting in the rural outback. These days, that image belies the 1980s reality of cheek-by-jowl suburban living, where the family car is a lifeline to shopping and work and where life is compounded by twice-daily rush-hour traffic jams that deliver people to their homes and jobs in a kind of stupor.

With Metro's arrival, Paul Hoshall, who lives in the Five Oaks subdivision, no longer will have to take the bus to Ballston and the Metro to McPherson Square (an hour-long trip) to reach his job at the Veterans Administration. Instead, he'll be able to ride the train from Vienna straight into town in 30 minutes.

But his enthusiasm over the new convenience is tempered by the expectation of hassles. He fears that the more than 2,000 parking places at the station won't be enough, and commuters will prowl the area looking for a space. "They're going to find out they can park on his street and walk over to the station," he said. "There's going to be a significant impact."

In neighborhoods nearer the station, the county is issuing parking permits to residents. Cars without the permits will be towed.

In Country Creek, a neighborhood of 352 brick town houses just northwest of the terminal, the streets are private -- not part of the state road system. Residents there have adopted a separate decal system, and are planning to have the cars of intruders who park on their streets towed.

In Fairlee, a neighborhood of 68 single-family homes just south of the station, fears of the local traffic, noise and development that Metro is expected to bring divided residents into two bitter factions -- one that favored selling its homes en masse to a developer, and one that wanted to stay put.

The two sides were barely talking for much of the spring. The matter was laid to rest -- at least for now -- when the county board decided last month that Fairlee would remain zoned residential for the time being.

Tom Schach was in the group that wanted to sell its homes in a block to a developer and move away. "Most of us are uncertain and scared of what Metro's going to bring," he said. "Foot traffic, people dropping off others, traffic coming through. Trying to get out of the neighborhood is a big problem. People are ready to escape, and they figured this was a good time."

One of Schach's neighbors, Charlotte E. Michael, was opposed to selling her home. "We celebrated with pink champagne" when the board decided not to rezone Fairlee, said Michael. "Oh, what a wonderful, beautiful night that was!" She said she will use the Metro station, which is just a minute's walk from her front door, to visit District art galleries and the Mall during cherry blossom season.