A silver Rolls Royce, about two inches long, is parked on a tree-lined street in the scale-model display at the Foxhall Crescents sales office.

It is inconceivable that a Ford or Chevrolet would appear in the display. When the houses sell from about $390,000 to over $450,000 on the estate once owned by the late Nelson Rockefeller on the District's exclusive Foxhall Road, only a Rolls will do. "extravagantly unique," "elegent" and "distinguished" are the adjectives used by the Dagmar Burton, the project sales manager, to describe the 120 detached houses that in five years will cover the 25 acres Rockefeller used to call home when he was in Washington.

The three-year history of the controversial development enters a new phase next week when the project builders, Crowell and Baker, start razing trees and landscaping the rugged terrian. Company president Arden Baker predicts that construction of the first house will begin within six weeks and should be ready for occupancy sometime next fall.

The cold war that pitted many of Washington's most distinguished citizens who live in the Foxhall area against the developers, Rozansky and Kay, now appears to have abated. The uproar over initial plans that neighbors said called for "ticky-tacky" homes was diffused when Alan Kay retained architect Arthur Cotton Moore in January 1978 to redesign the development.

"we chose Moore because, first he's a fine architect, and, secondly, be- cause he is well respected by many of the people who live around here," Kay explained. "he knows a lot of them socially and they trust him."

Moore conceded this week that he, too, probably would have objected to the originial "chekerboard" site plan, which called for houses to be built in symmetrical rows after most of the old trees that grace the property had been razed.

"i didn't want to produce "estateetes" Moore explained. "i wouldn't do any of the pseudo-colonial things you see out in Potomac."

What Moore and associate Barry Dunn arrived at were crescent-shaped clusters of houses, 25 to 30 feet apart, following the contours of the land. From there, the step back to 18th-century England was easy.

"the Royal Crescent in Bath was the most successful speculative development in history," Moore said. "you want an elegant image, and that fit."

Intense negotiations between developer and the neighborhood coalition formed to fight the project produced concessions on both sides.

Thirty percent of the trees on the property will remain in place, and a 30-foot buffer of vegetation will surround the property.

Kay, on the other hand, refused to reduce the number of houses he planned to build below 120.

Today, coalition leaders generally seem pleased with the changes, but promise to "keep a co-pilot in the bulldozer" as work progresses.

And who's going to buy the finished product?"the people interested in our houses are not going through the classified," observes Burton.

"admittedly only the very affluent, these superb residences will reflect the 18th-century English architecture mode which reached its zenith with the completion of the Royal Crescent at Bath, England, in 1775," pronounces one newspaper advertisement for the development.

Thanks to promotions like that, 16 of the initial crescent cluster of 26 houses already have been sold. The buyers largely are well-heeled professional couples who have built up equity from other houses and whose children are grown. Five of the 16 purchasers have opted for the "extra" of having their own elevators.

Not everyone equates a $450,000 price tag with luxury, though.

"these days, $450,000 buys you a garage in Washington," observed Basheyba, the colorful real estate broker who in 1976 first proposed to then-vice president Rockefeller the idea of selling the property.

At Foxhall Crescents, that amount of money will get you a very well appointed, three-story, four-bedroom house of about 4,200 square feet on less than a quarter acre of land.You will get a formal living room, dining room and kitchen-family room as well as walk-in closets, separate dressing rooms in the master bedroom and a two car garage, amoung other things.

Developer Kay readily admits that the money is spent on the location, with the rockefeller cachet thrown in for good measure.

"there's no question that the same house anywhere else would cost a lot less," Kay explained earlier this week. "the lots go from $120,000 to $150,000. If you built a house in West Virginia on a lot for $3,000, you could put the $120,000 difference into the house, and you'd have a lot more house."

Then again, the odds are good that the one in West Virgina would not have space included for an elevator, as each of the Foxhall Crescent houses will.

It probably would not have an oval whirlpool bath or a "cuisinette" wet bar in the library, complete with "mini" microwave oven to warm hors d'oeuvres "so you can take goodies out to the patio without sending up to the kitchen," as Burton explained.

Nor would it nesessarily have a fireplace in the master bedroom, a marble foyer with a circular staircase or an intercome system.

And it is doubtful that the house in bar in the library, complete with a limestone base, honey-colored brick (choice of shading), and arched Palladian windows strictly in keeping with the sweeping Royal Crescent building at Bath.

"it's the empty-nest market," Moore explained, grimacing at the term. "these are people who are returning to the city from the suburbs and place a preminum on entertaining. They want big living rooms which they're going to use a lot. This is not a 'recroom' crowd." "these are people who are leaving a $300,000 to $400,000 house and two acres in Potamac," echoed Kay. "they want a smaller house now that the kids are gone. They want less maintenance; they don't want to mow the lawn anymore. They want to be conveniently located to the downtown area, but they don't want a Georgetown townhouse."

Burton described the purchasers largely as doctors, lawyers, and men who own their own business -- " people of quality," as she puts it. Many are from the greater Washington area, although she claims to have received inquiries from Paris and California.

Kay would not disclose what kind of profit he expects to realize on each house. But when asked if he thought the $5.5 million he paid for the land and the long struggle against the neighborhood coalition was worth it, re replied, "Absolutely."

Yet knowledgeably real estate sources caution that the future of the $450,000 house market may be less than rosy.

"now that the prime lending rate is at 14.5 per cent, it's a whole new ball game." commented Robert Linowes, former president of the Washington Board of Trade.

"don't get me wrong, I think Foxhall will succeed," he cautioned. "people like the snob appeal and all that goes with the statement, I'm living on the old Rockefeller estate. But the overall picture is uncertain."

"you need cash-heavy people. That's the key to that market," added broker Samuel Scrivener. "that market can't depend on high interest rates. All of us involved in realestate are watching what happens at Foxhall Crescents very closely."