The District of Columbia's biggest enclosed shopping center opens today, a $100 million, 100-store complex tucked into the heart of Georgetown.

Behind the preserved and polished facades of the century-old buildings on the south side of M Street NW is a three-tiered retail revolution that will either lure $70 million worth of new business to Washington or go broke glamorously trying.

Georgetown Park -- "it's not a shopping mall, it's the world's first shopping park," says developer Herbert S. Miller -- is probably the most costly shopping center of its size ever built.

The tenant list runs from Abercrombie & Fitch -- opening in February -- to The Georgetown Zoo -- a stuffed animal shop -- and will enlarge the business district of Gerogetown by more than 25 percent, from 350 stores to 450.

With a mixture of embarrassment and enthusiasm, Miller admits the project cost "a lot more" than projected six years ago when his firm, Western Development Corp., formed a joint venture with Donohoe Construction Co. to rebuild the southwest corner of Wisconsin Avenue and M Street.

Donohoe found itself with what one engineering magazine called the most complicated construction job on the East Coast -- squeezing 100 stores, 300 parking spaces and 128 condominiums between the historic storefronts of Wisconsin Avenue and the sheer stone walls of the C&O Canal.

"As far as private enterprise is concerned, I can think of nothing that approaches it in complexity except Metro," said James Donohoe, vice president for sales and development of the family construction firm.

Preserving the 100-year-old facades on Wisconsin to placate local landmark lovers required encasing the storefronts in steel beams, propping them up with block-long braces and slipping new foundations under them. That alone meant $1 million in direct costs and delays, Donohoe said.

To maximize use of the costly site, the basement parking garage had to be lower than the bottom of the canal -- in 10 feet of solid rock that had to be dynamited away without tinkling the china of Georgetown's elite.

More steel struts and tons of concrete underpinnings were needed to keep the 10-foot thick, 35-foot-high canal wall, Clyde's restaurant and other aging structures from falling into the hole.

The job wound up taking 10 months longer than anticipated and cost "a substantial amount of money" more than budgeted, Donohoe said.

Having the general contractor as a partner helped, but Western officials still figure the final bill will come to $50 million-plus for the retail center, $25 million for the condominiums atop the shops and another $20 million in store interiors and fixtures.

Despite the construction cost overruns and financing charges that skyrocketed when the prime rate passed 20 percent, no corners were cut, Donohoe insisted. "It's first class all the way."

The expensive extras include wood-floored hallways instead of the usual terrazo or tile. "Wood feels better to walk on," explained Miller. The block-long skylight over the central courtyard is spanned by ornate cast iron braces, custom made to match the stanchions that support the brass rails around the balconies and the brass-and-glass elevators.

The exterior is Federal style, the predominant architecture of Georgetown, but the interiors are Victorian. "It's eclectic," Miller said, "but Georgetown is eclectic."

To pay the rent for such cushy quarters, stores will have to have annual sales of $300, $400 or even $500 per square foot, Miller said.

Most mall merchants figure $100 to $150 a foot is a good volume, and Miller admits "you have to be a better merchant" to succeed in places like Georgetown Park.

Georgetown Park's stores are smaller than those built by the same operators in other projects, they have smaller back rooms to dilute the sales per square footage and the approach to business has to be different, Miller said.

"In a mall you have department stores and everybody else feeds off them. If you don't have department stores, you have to do it on your own.

"Other urban centers are doing it," Miller added, noting that sales at projects such as Chicago's downtown Water Tower Plaza, Boston's booming Faneuil Hall and Baltimore's year-old Harbor Place are running in the $400-to-$500-per-foot range.

Comparisons to such successful urban retail developments draw disclaimers from Miller, who insists that "Georgetown Park isn't like any of them. Nothing is the same; there's nothing like this anywhere. Georgetown Park is the only Georgetown Park in the world."

Unlike Harbor Place, which is primarily a tourist attraction with recreation-related retailing, the Georgetown project "is for serious shopping," the developer said.

But if there are imperfections in Georgetown Park, it's not Miller's fault. Two days before the scheduled opening, he was preparing to throw out the hand-built oak kiosks on the main floor because they didn't "look right" and was wondering whether to white out the mural at one entrance for the same reason.

Extremism in the pursuit of profit is no vice to Miller, and moderation in the defense of historic Georgetown was not even a possibility when it came to designing the exterior of the complex.

Most of Georgetown Park is hidden away in the center of the block, behind a row of restaurants and an abandoned fire station. The visible portions of the project were forced into the Federal mode of the rest of the neighborhood.

While Miller boasts that Georgetown Park is the only shopping center in America with a national park (the C&O canal) running through it, the canal has been as much an albatross as an asset to the developers.

Not only did the Landmarks Commission order the $1 million facade preservation on M Street, but the National Park Service also dictated the design of the backside and the bridges linking the main building of Georgetown Park with its Canal House annex on the south side of the canal.

After extensive negotiations and over the objections of some residents' groups, the Park Service permitted the developers to cut an entrance at the bottom of the 35-foot-high wall along the canal to provide access to the towpath.

The towpath traffic feeds into the lowest of the three shopping tiers. The second level is linked to Wisconsin Avenue by stairs, and the top tier is on the M Street level.

The Canal House -- first phase of the project -- opened last year with a Conran's homegoods store topped by 35 condominiums, all of which have been sold.

Another 29 apartments will go on the market in November, and 64 more will be ready in the spring. Prices range from $150,000 up.

Miller said about 70 of the stores are expected to open today and 85 percent will be in business by Christmas. He said only a handful of the stores are not yet leased. None of the center's restaurants will be open at first, a shortcoming Miller blames on D.C. building and licensing hangups.

Among the stores opening later will be the first East Coast shop of Abercrombie & Fitch, the big New York sporting goods emporium that went bankrupt a few years ago and withdrew to Texas and California.

Though Georgetown Park does not have "anchor stores" like a conventional mall, it has a couple of larger stores that set the tone of the center and help draw traffic. The biggest will be the Georgetown branch of Garfinckel's, in a prime location behind one of the preserved facades on M Street.

The Ann Taylor shop -- also owned by Garfinckel, Brooks Brothers, Miller & Rhoads Inc. -- is moving down Wisconsin Avenue to a bigger location in Georgetown Park. Another immigrant is Scan, moving from Canal Square two blocks away.

Miller said the merchandise mix is heavier on apparel, especially top-of-the-line apparel, than most shopping projects. Among the stores opening Washington branches in the project will be Davison's of Bermuda; Cache, a women's high fashion shop from Miami; La Vogue, a Richmond women's wear store; Le Sac, a New Orleans boutique; Senor David, a Madison Avenue retailer of Italian men's wear; Shinera, a New York store specializing in Japanese furniture and accessories; Mark Cross, the leather goods store, and Godiva Chocolatier.

Standards such as The Limited, Casual Corner, Hallmark Cards and Radio Shack will also have stores in the project. CAPTION: Picture 1, Western Development Corp. president Herbert S. Miller stands on balcony overlooking interior of new $100 million Georgetown Park shopping complex; Picture 2, Georgetown Park's M. Street facade, which required complicated conservation methods to keep it in harmony with its neighbors. Photos by Gerald Martineau -- The Washington Post