Transit planners at Metro headquarters it often is assumed, earn their keep by putting rail stations where large numbers of people already live and work. In fact, that process can work in reverse, as in the case of the White Flint station on Rockville Pike.

Taking shape beneath a relatively quiet stretch of the Pike, the station is intended to help generate a small and carefully planned city above it, to encompass apartments, shopping malls, hotels and offices when it is completed in the late 1980s.

"In most other cases we're dealing with a previously developed location, as in Bethesda or Friendship Heights," noted John Matthews of Montgomery County's planning board. Future Metro stations there lie beneath the central business districts; White Flint's opens onto a patch of bare ground.

That has led transit planners to turn their usual task on its head: They hope to bring people, jobs and buildings to the station, not vice versa. It is telling proof of the clout Metro can wield in shaping the social contours of Washington's suburbs.

The station's site was selected 13 years ago as future rail lines were colored onto the planning maps. The spot was not the first choice, planners explain, but it was settled on because the station needed land for parking, good access roads and adequate distance between the stops north and south of it.

Certainly the trains, scheduled to begin running when the Red Line is extended late in 1983, are not the only factor in drawing developers to the station's fringes, but they are hardly a liability. One real estate agent said he feels the station has brought expectations of rising property values to land owners and prospective buyers.

Already, townhouses and office blocks have sprouted near the station, which is just south of the Pike's noisy intersection with Old Georgetown Road. By the standards of what is to come, however, the site is still rustic.

Last month Metro announced plans for its largest development project to date: a $214-million complex of shopping malls, a hotel and 765 residential units on 33 acres next to the station site, which the transit authority owns. It would include parking for 500 vehicles and a carefully crafted network of ramps and drop-off platforms for commuters heading to and from the trains. Across the Pike would be 1,000 more parking spaces.

On a 12-acre plot across the street to the south, the owners of the White Flint shopping mall plan a new commercial development, to be called White Flint North. It would contain 300,000 square feet of office space, a 350-room hotel with confrerence facilities and retail space. After the mid-1980s, 200 apartments and 250 additional hotel rooms might be added.

Across the Pike, another developer plans a condominium project of 850 units, planning officials say. Adjacent to the Metro site on the north is another tract of land authorized for 350 more apartments, though to date the owner has not announced plans to build.

Add to that a two-story maintenance and parking garage Metro is building for 250 buses, the county prison system's pre-release center and on-going construction of private residences nearby, and the result is a major new population center in Montgomery County.

Matthews estimates that approximately 4,000 people would live in the major apartment projects now envisaged. About 500 might be staying in the hotels at any given time. Perhaps another 1,400 people would work in the buildings, and 450 more would be connected with the Metro-bus garage.

After the Red Line is opened through to Shady Grove, Metro planners predict, about 11,300 people a day will catch trains at White Flint and a like number will arrive there. Of those boarding trains, some 3,000 will come to the station in cars.

Despite planners' desire to rein in growth in many areas of the county, they view White Flint as an exciting challenge. As the North Bethesda Sector Plan notes in glowing terms, the site offers a "unique opportunity, present nowhere else in Montgomery County" to generate new housing and jobs.

The sector plan was adopted in 1978 after a lengthy struggle in the courts and hearing rooms involving Metro, private developers, then planning board Chairman Royce Hanson and civic groups. The plan authorized extensive construction along Rockville Pike, in line with the county's long-range efforts to create "corridors" of development and "wedges" of relative quietude.

Some civic activists, such as Allen Bender of Randolph Hills, feel their side lost the planning battle and should not try to fight it again. Noetheless, a first-class civic tussle could ensue if residents' groups pore over architectural designs now being drafted and argue -- as they are hinting they may -- that they do not fit the sector plan's guidelines.

Classic allegations against developers are being heard again: Metro is building a significantly different bus garage than what is promised it would build, it is said; planning officials have shown bad faith by going for the maximum density allowable under the sector plan.

"The whole area is going to look like Rosslyn, Virginia, one of these days," complains Chester Flather, president of the Garrett Park Estates/White Flint Park Citizens Association. "I'm not a professional planner, but I think I know what makes sense."

Traffic is a major concern of the neighborhood groups. Sector-plan studies maintained that with expansion of roadways and proper traffic management, rush-hour traffic on the Pike could be held roughly to its current congested, but not intolerable, volumes.

Though more people would be working and living in the area, the sector-plan report said, large numbers would ride Metro trains and buses, thereby preventing a major increase in private auto traffic. In fact, in their calculations, planners assumed no increase in rush-hour traffic in the years 1983 to 1988.

Civic groups challenge such contentions. They foresee paralytic traffic jams in the so-called "Terrible Triangle" formed by the Pike and two other major arteries, Old Georgetown Road and Nicholson Lane.

Flather suggests that those who buy homes in the new tracts south of White Flint could be disappointed. "I just wonder if they know what's in store for them a mile or two up the road," he asks, and adds that traffic jams between home and the station could discourage use of Metro transportation.

White Flint's ultimate layout is far from settled, however. On July 16, public hearings on the Metro developers' request to rezone their 33-acre site "transit station-mixed" are scheduled. The civic groups will get another day in court.

Thought the opponents may succeed in reversing what they see as the most objectionable features, Metro and private developers are equally determined that something big will be built on the White Flint site. If they succeed, Rockville Pike will be transformed that much further from the winding country road it was as late as the 1940s.