The Crystal City underground is no longer the Crystal City underground. Now it is called the Crystal City Shops@1750, a stab at grafting 21st century chic onto a warren of concrete.

Potbelly Sandwich Works and Subway are replacing locally owned lunch spots, and the executives at Charles E. Smith Commercial Realty have taken a break from negotiating leases to proclaim "Crystal City rocks," a point emphasized by their sponsorship of an upcoming street festival featuring the rock band Big Bad Voodoo Daddy.

The rebranding of Crystal City, a product of 1960s design, heavily dependent on Pentagon leases and the button-down corps of contractors who followed them, has begun. It encompasses an urban hipster marketing campaign and an evolving plan to begin ripping down some of its oldest structures.

At the six-building office complex formerly referred to as Crystal Plaza, Charles E. Smith is renovating two of the office buildings, but is studying whether to tear down the other four and start over.

"Our land as a raw development opportunity is worth more than the land encumbered by a tired building," Vornado Realty Trust, parent company of Charles E. Smith, said in its 2004 annual report.

"At the time, this is what was avant-garde in urban planning," Mitchell N. Schear, president of Charles E. Smith, said of Crystal City. "It looked and felt like a series of office parks. We are trying to give it a more urban feel."

As a major building owner in Crystal City, the company has a large stake in furthering its transition from de facto federal office park to a competitive player in the market for private business tenants, snappy retailers and the nighttime restaurant trade. The company has taken the lead in a campaign to try to put the area on a par with Clarendon or Bethesda, promoting "the hottest line-up of destination restaurants and eateries, all on a dynamic new 'Main Street.' "

The urgency for Charles E. Smith and others with a major investment in Crystal City has become clear: In the past two years, three important economic props have been shaken. The U.S. Patent and Trademark Office is vacating 1.9 million square feet of office space and moving to Alexandria; US Airways Group Inc.'s proposed merger with America West Holdings Corp. could send hundreds of local jobs to Arizona; and the Pentagon has recommended shifting its personnel from leased offices to more secure sites on military bases. That step alone could cost Crystal City as much as 3 million square feet of office leases, and more if government contractors follow their clients.

The confluence of bad news has accelerated a debate about the viability of Crystal City's original build-it-dense-and-lease-it-to-the-government philosophy, and has led Charles E. Smith, local officials and others to start laying new plans.

The Pentagon's recommendations feel "as if a neutron bomb dropped in the region," Gerald E. Connolly, chairman of the board of supervisors in neighboring Fairfax County, said to fellow elected officials at a Northern Virginia Regional Commission meeting on May 26. "It will have ripple effects on all of us."

In the early 1960s, pre-Metrorail, the land now known as Crystal City hosted railway lines, a brickyard, and acres of industrial wasteland. It had two good physical assets: It was across the 14th Street bridge from downtown Washington, and it was across what is now I-395 from the Pentagon.

A group of investors, including real estate developer Robert H. Smith, acquired 18 acres of land in 1961 and started to build a utopian vision with Crystal House, an 800-unit apartment complex that featured an elaborate crystal chandelier in the lobby. The now 150-acre development hosts more than 10 million square feet of office space, 12,000 parking spaces, 6,500 hotel rooms, and more than 5,000 residential units.

The development was much a product of its time, with efficiency prized over imagination in the look of the buildings and the use of the surrounding space, and underground tunnels judged an adequate substitute for an attractive streetscape. In urban renewal fashion, Route 1, Jefferson Davis Highway, runs through the complex.

"Crystal City is interesting, because it could have developed as a downtown," said Robert E. Lang, who directs the Metropolitan Institute at Virginia Tech and recently wrote a book, "Edgeless Cities: Exploring the Elusive Metropolis." "It has transit and a grid of streets. Instead, it was developed in a modernist theory where you separate people from the street."

The minimalist style may have seemed appropriate for Crystal City's military-oriented tenants, but may make it harder to compete for private-sector business with newer office complexes in Fairfax, Montgomery and other nearby counties.

"There's not a ready market for those buildings. It will take a long time to reposition that space," said Stephen S. Fuller, a George Mason University professor who analyzes the Northern Virginia economy.

Crystal City business and government leaders say they recognize the problem. According to Vornado Realty Trust's filings with the Securities and Exchange Commission, government agencies rent 42 percent of Charles E. Smith's commercial real estate, generating $186.3 million in revenue for the company. Government contractors rent another 29 percent. With the patent office's departure, the company has begun a $150 million makeover and re-leasing plan, which includes new mechanical systems, bathrooms, lobbies and corridors at 2100 and 2200 Crystal Drive, according to the SEC documents.

In front of the two buildings, Crystal City's next phase is taking shape: a $43 million addition of retail space, with sidewalk restaurants and glowing neon signs. Crystal Drive, part of a network of one-way streets that has frustrated visitors, has been rerouted for two-way traffic to make the area more accessible.

Ideally, local developers say some of the same things that made Crystal City practical to begin with -- easy access to I-395 and Reagan National Airport, plus its own subway stop and regional rail station -- would be strong selling points in a region increasingly worried about sprawl and long commuting times. Already, the Public Broadcasting Service and the Federal Supply Service have signed leases for some of the space vacated by the patent office.

"What you have got in Crystal City -- you've really got one of the only quote-unquote suburbs where, when you park your car in the morning, everything is a walk-to amenity," Schear said. "When you're in Tysons [Corner], you have to get in and out of your car."

Local officials note they have time to make the adjustment.

The Pentagon's changes are "over six to 10 years," Arlington County Board Chairman Jay Fisette said. "If it were all to happen in one year, the impact would be very significant. Either way, it's a large number of people."

Still, shop and restaurant owners in the area say the fall-off in business has been noticeable since the patent office departed, and they worry the slowdown will continue as U.S. Airways and then the Pentagon begin withdrawing from offices.

In an area that is slowly becoming populated with Starbucks, Quizno's, and higher-end restaurants such as McCormick & Schmick , convenience store owner Steve Yong said that small businesses can't wait a year or two or three while the area establishes its new identity.

"Almost six months ago, I had customers all day long. But not now," Yong said. "Crystal Park Two is almost empty now. . . . I try, I try, but I'm not sure [he can stay in business]."

Vornado representatives recently held a meeting with shop owners to explain their new advertising campaign, and highlighted ways for them to promote their businesses.

Some shop owners said, however, that they can barely afford the rent, let alone additional advertising costs.

Chevy Chase Bank Assistant Branch Manager Julie Kim said bank business has taken a dip. As she sipped a beer at Hamburger Hamlet in what used to be called the underground, she said Crystal City has always been one of the area's hidden gems -- even if it isn't exactly rocking yet.

"If I call up my girls to go out," Kim said, "we're not going to think of Crystal City."

Mitchell N. Schear oversees Crystal City's makeover.Crystal City, seen from the Potomac railroad yard near U.S. Route 1 in 1983, featured office buildings for federal tenants and their contractors. Many now face possible relocation to military bases for security reasons.The Crystal City area is undergoing a renovation to make it a shopping and entertainment destination. As major stores and restaurants arrive, however, some local merchants wonder if they can afford higher rents.