When Marcia Humbaugh moved to Kingstowne this summer, she did not bother to meet the neighbors.

There weren't any.

As the first resident in a development that one day will accommodate 15,000 people, Humbaugh's companions were a lone security guard and the dirt bikers who occasionally roared over the scarred, empty hills.

"It felt weird," said 39-year-old Humbaugh, owner of a $167,000, two-story house in the development near Franconia in southeastern Fairfax County. "It's so close in {to Washington}, but there's a lot of land out here undeveloped. That's what's strange."

The 1,170-acre residential and commercial project, where heaving construction trucks make up much of the rush-hour traffic, represents a sliver of history for Fairfax.

It is the last of the megadevelopments in the county, a $1 billion mixed-use project that many developers say signals an end to the boom-town frenzy of growth that has characterized the Washington region's most prosperous and populous jurisdiction.

When completed, Kingstowne will rank third in size, behind the planned communities of Reston and Burke Center.

"You'll not see another Kingstowne or any other planned community of that size in Fairfax," said Gordon Smith, president of Miller & Smith Inc., the development firm that sold the property for $30 million to Silver Spring builder and developer Warren Halle. "From a developer's point of view, the county is basically developed."

To assemble such a large chunk of land "is almost impossible in the greater Washington region," said R. Robert Linowes, a land use lawyer who has worked on large-scale developments in Washington and suburban Maryland. "Individual parcels are being developed separately rather than under one ownership."

According to Francis Steinbauer, a senior vice president of the Henry Long Co. and a past president of the Mobil Land Development Corp., which owns Reston, "It certainly would be the last of its size . . . . They have an opportunity to do something that is special."

In Kingstowne, which stretches from near Franconia Road in the northeast to Beulah Street in the southwest, lights shine in homes where 165 families now live.

The community's first settler has watched her street almost fill up. "Everybody waves," Humbaugh, a technical information specialist for the Environmental Protection Agency, said of her neighbors.

Hundreds of houses in Kingstowne are skeletons of what they will become. The proposed town center, on the planned Kingstowne Boulevard, is a swath of rutted red dirt, framed by towering power lines and a big sky -- reminiscent of a Texas landscape.

Looking over the jumble of wooden planks, concrete and bare land, developers envision "a city" with 43 neighborhoods

when the project is completed in 10 to 15 years.

The community will consist of 5,500 housing units in a mix of styles, priced up to $210,000, a town center with about 2.1 million square feet of office space and a 164,000-square-foot shopping center, a 74-acre park, two recreation centers and a 14-acre lake.

"We're trying to attract people looking for a terminal city environment," said Bruce Thompson, a spokesman for the Kingstowne developer. "We don't want them to pass through Kingstowne to get someplace else. We are trying to create an employment center and a residential center."

The recreational amenities are eagerly awaited by Humbaugh, a "modified extrovert" who enjoys skiing trips in the winter and a Rehoboth, Del., beach house in the summer. After learning about Kingstowne, she said, she quickly decided to sell the three-bedroom brick rambler she had owned in North Springfield for 10 years.

"I wanted something all new, all young, all fresh," she said. "This to me seems like a last chance."

Long before Humbaugh discovered Kingstowne, elaborate schemes were being laid for the property. The land once was a series of gravel pits that served the District of Columbia.

The most grandiose plan came in the mid-1970s. A developer from New York City conceived of "New Franconia," an intensely developed planned community encircled by a monorail. The people-mover would transport residents to cosmopolitan shops and offices in the development.

"When it came to financing, it didn't make sense. It was far out," said Smith, who eventually bought the property.

Depending on circumstances, primarily the economy, Kingstowne's final incarnation remains to be seen. Already, the project has experienced the best and worst of a developer's dreams.

Kingstowne was formally endorsed by the county government in June 1985, with not a peep from the residents who live in the nearby well-established neighborhoods of modest houses and steepled churches.

During the previous 18 months, however, a panel of residents had scoured the developer's plans and wrangled about 150 concessions. It was apparently a record number of commitments from the developer to provide amenities that include $18 million in road improvements. Among the commitments is the construction of 1 1/2 miles of South Van Dorn Street from Franconia Road to Telegraph Road.

Robert McLaren, a nuclear engineer who served on the citizens advisory group, recalls the tedium of sorting through the developer's voluminous documents: "I shudder when I think of it."

In the end, McLaren and other residents were satisfied.

"It's going to be a positive influence in the area, given the fact that the land would have developed anyway," McLaren said.

The rough stretch of land was basically the county's backside.

After the gravel pits were worked out in the early 1970s, the property had become a dumping ground for balding tires and discarded refrigerators.

"It looked like the last visitor to the area was Neil Armstrong. It looked like the surface to the moon," said Dana Kaufman, administrative aide to county Supervisor Joseph Alexander (D-Lee).

The land was owned by the Lehigh Portland Cement Co., which in the late 1970s became a subsidiary of a German firm in search of an American investment, according to Smith, the former developer. The firm held a tight grip on the land for almost a decade more.

In 1984, Smith called the company. He wanted to buy 74 acres on which to build apartments. When his offer was rejected, Smith said, he decided to go all the way.

In an extraordinary land deal, Smith said, he wrote up a four-page contract for the 1,170 acres himself and negotiated most of the $13 million purchase over the telephone.

"The negotiations were almost nonexistent," he said. "It was the simplest contract I ever did for the largest piece of land I ever bought."

Fairfax County planning commissioner Carl Sell said he admires Smith's business acumen. "He's a pretty shrewd negotiator. He'll be like the guy with the holes in his shoes. He doesn't want to appear like he has too much money."

Two years later, in a move to diversify, Smith's company sold the property for $30 million to Kingstowne Limited Partnership.

Its new owners have had their share of difficulties.

Twice in the past year and a half, the county has come down hard on Kingstowne because of inadequate erosion and siltation controls.

Kingstowne construction sites were ordered to shut down in September 1986 and this summer after heavy rains caused severe erosion and siltation problems that threatened environmentally sensitive areas, including nearby Huntley Meadows Park, one of the region's largest wetland areas and home to dozens of species of birds and fish.

"If their priorities were different, they could have prevented the siltation {problems} they had. They were taking a chance and got caught by the rains," said Ed Jankiewicz, an official in the county's Department of Environmental Management. "If you do the other type of work we're interested in, it's not a salable item. They were looking to recover cost and develop sections that will sell."

But Kingstowne officials fought back. The developers filed an injunction in Fairfax County Circuit Court in September, charging, among other things, that the county had caused "grievous financial loss and compensable diminishment in reputation to Kingstowne."

Since then, the environmental concerns have been remedied, the legal papers have been withdrawn, and the planned community has developed at a brisk clip, according to county and Kingstowne officials.

Fairfax officials hope that Kingstowne will infuse energy into one of the oldest housing areas in the county. They expect the project to draw outsiders there for an estimated 10,000 jobs and recreation and cultural activities.

"They are in shape now," Jankiewicz said. "We just won't allow them to get off track. We watch it closely."

Meanwhile, Marcia Humbaugh, the newcomer, is sounding more like an old-timer as she settles into her airy, high-ceilinged home. She said she has found the kind of satisfaction in real estate that some people find in careers.

Now, she delights in her fourth real estate investment, frets over wallpapering and laments that thousands of residents eventually will become her neighbors.

"I think it's going to get very crowded," she said, cringing a bit for the first time.