Two miles west of Fairfax City, along Lee Highway, the woods are rich with red, gold and orange of the fall foliage.The forest and fields bordering the highway are dotted with housing subdivisions, small, independent businesses, old homes and a few farms.

This sleepy, semi-rural setting - just beginning to feel the encroachment of suburban sprawl - may be the future home of Fairfax County government. A 266-acre tract of woods and meadows known as the Smith-Carney site is the first choice of a special citizens' committee to be the future home of county government, now located in nearby Fairfax City in a 12-story glass and concrete tower called the Massey Building.

The Fairfax Board of Supervisors, while eyeing the site with a great interest, will not make a decision until it hears from the public at a Nov. 15 hearing.

The citizens' committee has urged the board to buy a new government site immediately. It warned that if the land is not acquired soon, fast-growing Fairfax County may lose the chance to find a centrally located site for the headquarters. The new headquarters would be designed to house the expanded local government expected by the turn of the century.

Even if the supervisors choose the $5.7 million Smith-Carney site over another nearby tract they are considering - called "West of Fairfax" and located just south of Rte. 50 - the vast and dramatic changes expected to accompany the move would not be felt for at elast 10 years.

Change, not as dramatic but just as vast, is already approaching this sparsely populated rolling ridge. Construction of subdivisions, townhouses, garden apartments and warehouses is planned on and around the Smith-Carney site, located between 1-66 and Lee Highway, if the county government does not move there.

This type of building, similar to the development that covers most of Fairfax County, would swell the area's present population of 5,000 to approximately 31,000 within 20 years, according to an extensive report by the board-appointed committee.

Meanwhile, a trim golf course across I-66 from the Smith-Carney area has been uprooted to make way for a mammoth 137-acre shopping center called Fair Oaks Mall. The center, which has been compared to Montgomery County's White Flint, will hold 125 stores when completed in 1980, making it Northern Virginia's second largest shopping center. The Tyson's Corner complex is the largest.

"Nobody's jumping up and down all excited about the (government) center coming here, but they're not jumping up and down about any kind of development," said paul Black, a resident of Dixie Hills, the neighborhood that borders the Smith-Carney tract. "People obviously would like to see things stay as they are."

Some residents of the 104 homes that make up the four small subdivisions closest to the Smith-Carney site vigorously oppose the location of the government center there. But msot appear to be resigned to the inevitability of growth.

The question most residents face is whether they would prefer a government center to apartments, town-houses and other homes that would be built at a higher density than their own neighborhood, in which homes valued upwards from $60,000 occupy spacious, wooded lots no smaller than one acre.

"We know Mr. Smith and Mr. Carney, whoever they are, don't own all those acres just to donate to our neighborhood as a bird sanctuary," said Dixie Hills resident Ellen Waterman, whose back yard ends in a wooded ravine that buffers her home from the proposed government site. "I'd rather see the government center out there, I think, than a lot of apartments and condominiums."

The coming of the center would transform the Smith-Carney vicinity into an employment and commercial hub attracting more than 10,000 employes. Area traffic, already heavy with commuters along Lee Highway, would increase by 21,000 to 56,000 cars a day if the center is constructed, according to the citizens' report, and would require a cloverleaf and another large intersection on Lee Highway to provide entrance to the complex.

These and other traffic improvements, along with construction of the center, would destroy four older houses along Lee Highway and a farmhouse, once the focus of now-unused farmland inside the Smith-Carney tract, county officials said.

In addition, the increasing value brought by commercialization of the land probably would mean the eventual replacement by higher density housing of about 95 other old houses on the south side of Lee Highway, the report states.

Preliminary designs of the government center show a campus-like layout of several low- and mid-rise buildings spread over the rolling farmland and hardwood forest. Much of the 266 acres would be preserved to protect fragile soils and a stream valley, and parking lots would be small, scattered and landscaped, the report shows.

"The site is a beautiful one and an asset that should be used instead of obliterated," said Michael Horwatt, a Reston lawyer who chaired the citizen committee. "There's no reason the center should't be planned as an advantage to the area."

Law offices, banks, consulting firms, shopping facilities and other government-related commercial offices are expected to spring up on 33 acres east of the Smith-Carney site on Lee Highway, displacing what would have gone to warehouses and light industrial uses.

"Realistically speaking, we can't remain the way we are now," said James Donovan of Legato Acres, president of the Dix-Cen-Gato civic association, which represents the four subdivisions next to Smith-Carney.The development that suits the needs of the county and safeguards the interests of the community."

Fairfax Supervisor James M. Scott has suggested a public contest to choose the architectural and landscape design of the new center.

The country views new government headquarters as the solution to spending nearly $1 million a year to rent space in Fairfax City and elsewhere in the county. The citizens' committee said the county could save nearly $50 million during the next 40 years by relocating the government out of the city.

Scott's proposal, as well as proposals on how the county should acquire whatever site is chosen, also will be discussed at the Nov. 15 hearing at Robinson Secondary School.