The developers who 70 years ago founded Northwest Washington's elite Spring Valley neighborhood launched an experiment in housing, an effort to break the District's mold of row houses and gridded streets, and to create not just a cluster of luxury houses but a community as well.

It was back in the late 1920s, and the District and other large cities were being buffeted by change. Washington's old neighborhoods were fading, and white residents were feeling crowded by an influx of immigrants and threatened by the movement of African Americans into some traditionally white neighborhoods. There was a demand for new housing. Developers William C. and Allison N. Miller, native Washingtonians, saw an opportunity in some hilly, untouched land close to the Maryland line. The natural springs that fed a creek on that land led the brothers to name it Spring Valley.

Their grand experiment succeeded--although the racial and religious restrictions that governed purchases there, as elsewhere, are long gone. The large, comfortable houses the two brothers built sold well from the beginning and have greatly increased in value over the decades. The Millers had planned for 161 houses but never felt hurried to complete the development. Now, many years after their deaths, the fourth generation of the family is finishing the work with the sale of the remaining 19 lots.

All these years later, it's hard to look at some parts of Spring Valley and think of it as a "development" as we know them now. Heavily wooded land rises and falls; houses peer down over winding streets from the brow of a hill, or are tucked into a leafy depression below the road. A rocky, wooded ravine picturesquely splits one of the neighborhood's main boulevards.

The remaining sites, and the houses near them, have a more typical suburban look: street, sidewalk, lawn, front door. The last are located in two cul-de-sacs, and a few are clustered along one street, according to Karen S. Krupsaw, vice president of marketing.

There is a sense of nostalgia as the company completes one of the first communities the late Miller brothers began, Krupsaw said, but there are other projects underway.

"We are growing very rapidly as a company, and we are building some great new neighborhoods," she said. "We are working on a site called Willard's Ridge in Bethesda, and we have a number of individual lots in the area. We sometimes buy an existing house with an adjoining lot and build on that."

The Miller brothers grew up in Cleveland Park. When they were young men, their mother gave them $2,000 and two vacant lots on the 700 block of Kenyon Street NW as an incentive to go into business, according to a company history. They created W.C. & A.N. Miller Co. in 1912 and began to build houses in Northwest Washington as well as a commercial building in Georgetown.

Business was interrupted when the brothers went into the service in World War I. On their return, they purchased parts of what is now Wesley Heights near American University and built upscale town houses along the hilly streets. They converted an old house into a community center that was extensively used by residents for dances, baby parades and picnics.

They would offer a community center again in their next big project, Spring Valley, when they began work there in 1929. In keeping with the formal segregation of the day, the Millers determined that Spring Valley would be an exclusively white community. Trying to attract lawyers and bankers and members of Congress, they specifically barred African Americans and Jewish people from purchasing houses.

Other neighborhoods in the District had done the same. LeDroit Park, near Howard University, was an early gated community that was for white residents only. In Southeast Washington, Uniontown--now called Historic Anacostia--was built to house Navy Yard workers, and those developers barred African Americans and Irish Americans from living there.

All such convenants were struck down nationwide in 1948 when the Supreme Court ruled they were unconstitutional.

It was probably clear from the beginning, though, that the elegant community the Millers created in Spring Valley didn't need those hated--and now embarrassing--restrictions. Getting into Spring Valley required the ultimate discriminator: money.

From the beginning, the four-bedroom, two-bath houses carried high price tags. The first houses sold for $60,000 in 1929. Last year, some of the early houses, as well as those built later in the century, sold for an average of $780,000.

These were not postwar tract homes. "Everything was custom then," explained Krupsaw, who pulled from the Miller archives the blueprints for a porticoed, colonial-style manse built in 1929. The house is rich in detail--built-in bookcases, window seats, a serving pantry, an ironing board built into a cabinet in the kitchen. And there is a buzzer on the floor in the middle of the formal dining room, echo of a time when there would have been someone out in the kitchen to answer the call for the next course of the dinner.

That house is currently assessed at $1.6 million.

Many later houses were more modest, but larger ones will be built on the remaining lots and are priced from $800,000 to $1.75 million, said Michael Seay, a company vice president and director of sales.

The business has been kept under family control, according to company literature, and is now owned by 40 minority stockholders, all descendants of the founders. A fourth generation has taken charge--Edward J. Miller Jr., as president and chief executive.

Seay, who is married to Edward Miller's sister, Frances, said he recently sold his house in Potomac to return to Spring Valley with his wife and five children. Like his father, he was raised there. They even had the same fourth-grade teacher at Horace Mann Elementary School, he said.

"There is a creek called Old Mill Creek where I used to play in the 1950s," he said. "It wasn't deep enough for swimming, but we could wade in it. Now my children are going there."

Seay and others have found Spring Valley a good place to raise children because there are no through streets; instead the residential roads meander along the natural contours of the land.

The Millers broke a long-standing regulation that the street grid established by Washington city planner Pierre L'Enfant in the 1790s was to extend throughout the District. At the time, curvilinear streets had become the fashion in upscale subdivisions across the country. The Millers had little trouble convincing the National Capital Park and Planning Commission of the aesthetic benefits of abandoning the grid.

There are few parts of the District that have so totally escaped the mandatory grid. On a map of the city, Spring Valley's streets resemble cooked pasta, with strands intermingled in loops and turns. The design also had the benefit of foreclosing the possibility of any thoroughfares bringing in unwanted traffic and outsiders.

The boundaries of Spring Valley are Massachusetts and Nebraska avenues, Loughboro Road and Dalecarlia Parkway NW. American University and Dalecarlia Reservoir form the east and west boundaries.

The Millers planned Spring Valley carefully. They studied the best suburbs and subdivisions in the country, including J. C. Nichols's Country Club District in Kansas City, Kan., the Van Sweringen brothers' work in Shaker Heights outside of Cleveland and the Russell Sage Foundation's experiment in the Forest Hills section of the New York borough of Queens, according to an article by historian Diane Shaw Wasch.

In each case, the Millers found that the developers had gone "beyond mere speculation to create a special kind of community--a community of harmonious building styles and landscaped streets, a community of like-minded homeowners with family values, a community with a chance for survival," Wasch wrote in "Washington History," a publication of the Historical Society of Washington.

W.C. Miller wrote about accepting this challenge in an article in the National Real Estate Journal, saying: "The most progressive subdivider has become a builder. He is developing the home and the home site complete. . . . We went further than the subdivider generally goes and went into the class of community builders. This is a step in the right direction and America will be the better for it."

CAPTION: Chief executive Edward J. Miller Jr., in front, and other executives outside the W.C. & A.N. Miller Co. offices in Spring Valley. Behind him, from left, are William Miller, Michael Seay and Allison Miller.

CAPTION: Spring Valley in the late 1960s showcased the picturesque neighborhood's characteristics that still are evident today: heavily wooded properties with large houses that overlook winding streets from atop a hill.