Right now, they are little more than massive slabs of gray concrete jutting out of the clay, swarmed over by heavy bulldozers and construction crews readying them for an estimated 46,000 daily commuters by early 1986.

But there's no mistaking their ultimate purpose: They are the two Falls Church Metro stations -- neither of which, it so happens, lies within the two-square-mile city's limits.

And that's just fine with Falls Church.

The West Falls Church station will be in Fairfax County; the East, in Arlington.

The two Falls Church stations, which were christened after like-named stations along the now-defunct trolley line from Rosslyn to Fairfax City, are on the Orange Line, which will eventually terminate just outside Vienna. (It now ends in Arlington's Ballston area.) And, like all the stations on the Orange Line west of the Ballston stop, these two are being built in the median strip of I-66, which opens later this month.

Both stations are about 65 percent complete and will be finished before 1986, officials say -- though there are no estimates as to when. Yet neither will open until the Dunn Loring and Vienna stations do, largely because of opposition by Falls Church.

Falls Church officials are worried that their tiny residential city would be inundated by the traffic that would come if Falls Church were even temporarily at the end of the line.

Arlington, meanwhile, stoically absorbs the end-of-the-line congestion at Ballston.

Even so, residents of Falls Church weren't the only ones to be concerned about the possible adverse impacts of the stations.

"On the whole, we are satisfied that all has been done that's possible to do to protect our neighborhood," said Fairfax County resident Phil Zanfagna, a former county planning commissioner who was active in negotiating safeguards for his Idylwood Road residential community near the West station.

"It's supposed to decrease traffic from here to the District and on out [to Vienna], so our association worked along with it and got the landscaping and things we wanted," said Carl H. Hilley, past president of Arlington's East Falls Church Civic Association, who lives four blocks from the East station. "There have been no real complaints about it."

But the changes that many have expected as a result of the stations are already becoming apparent.

The East Falls Church station in Arlington, which had a bid price of $8.1 million, is in the I-66 median, with access from Sycamore Street and Washington Boulevard. The immediate area, on the northern fringe of the county, is undergoing transition. Town-house developments have sprung up in recent years, providing a buffer to the single-family neighborhoods. But the area also has several run-down service industry and commercial establishments. They are expected to give way as the value of the land on which they are situated increases and drives up property taxes on the establishments.

Arlington planner Suzanne Fauber said it is expected that such businesses will eventually be replaced by more town houses and limited commercial development in the form of four-story office buildings.

"It's very important that we try to act together with Falls Church because a lot of people perceive that area as being more a Falls Church atmosphere than an Arlington one," Fauber said. The area "should be compatible with Falls Church, so they have nothing to fear as far as another Rosslyn, Ballston or Clarendon coming into that area."

Falls Church already is feeling pressure from developers, although the city has a strict seven-story height limit, said chief planner Henry G. Bibber. "We're not looking at Rosslyn-type development here, but at improving the industrial and commercial areas. We don't intend to make any changes in the single-family areas," he said.

Bibber said developers are looking at two sites: the so-called Kiessling and Beeson tracts off Haycock Road near the West Station, both of which are adjacent to an area Fairfax County is considering for possible low-density development.

Although the city expects to benefit from the stations and the increased land values accomanying them, Bibber said, Falls Church will remain "very vigilant and prevent heavy traffic from developing on residential streets."

The city already is developing contingency plans to ease traffic flows, especially along Broad and North Washington streets, the major thoroughfares, and is exploring the feasibility of station-to-station bus runs to accommodate city residents.

The city's George Mason Junior and Senior High School, separated from the city by Haycock Road, escaped the potential ravages of proximity to the West Falls Church station because of careful negotiations, Bibber said.

Haycock Road, off Rte. 7, and a Rte. 7 ramp from I-66 are the major access roads to the West Falls Church Station, which had a bid price of $11.5 million. John Rice, a Fairfax County planner, said there are "absolutely no plans" to disturb the residential area off Idylwood Road to the north of the station.

Although county plans are preliminary, Rice said, Fairfax is anticipating that it may want to encourage a multi-use mix of small office buildings and town houses, tapering them down in scale on the southern side near Haycock Road.

"It would not be like what you see at the Arlington stations," he emphasized. "And as you approach Haycock, any development would be scaled down."

Metro planner Earl Long said the lengthy negotiations between citizens and an assortment of local, state and federal officials over the design of the West station was a "textbook example" of cooperation that has led to "probably the most environmentally tuned rail yards of any subway system."

The interchange of Rte. 7 and I-66 was designed to avoid a number of problems, such as adversely affecting Falls Church's high school. The creation of a special high-speed bus lane from Dulles that enables buses to pick up and discharge passengers at the station without mixing with automobile traffic there is another carefully designed feature.

That design, said Long, will result in the West Falls Church Station becoming the Metro terminal for passengers bound for or returning from Dulles.

It will be, he said, "Metro's international entrance."