When callers ask directions to the Tycon Courthouse office building in the maze of bustling Tysons Corner, receptionist Stephanie Olmstead tells them to look for the structure with the horseshoe arch.

"That's usually what I tell them. After all, I'm supposed to be polite over the phone," she said. "All of my friends call it the Tidy Bowl building because it looks like a toilet bowl."

Like its striking counterparts throughout suburban Washington and across the country, Tycon Courthouse has left an indelible mark on the changing skyline.

Whether it's the "toilet bowl building" or a second Tysons Corner edifice dubbed "the brick shopping bag," or the so-called "Darth Vader building" in Prince George's County, distinctive structures are increasingly serving as signposts in the suburbs.

As some communities have blossomed from mostly one-dimensional residential neighborhoods into dazzling economic centers, many suburban office buildings no longer resemble bland, shoebox-like structures, according to urban planners, architects and members of the development community.

The trend has been toward "screaming architecture" -- signature buildings that function like billboards, according to Doug Porter, director of development policy research at the Urban Land Institute in Washington. The institute is conducting an extensive study of suburban activity centers nationwide, including Bethesda and Tysons Corner.

"One of the desires is to be highly visible and recognizable," Porter said. "It's happening all over the country, where you've got urban aggregations beginning to occur along major highway systems."

Ordinances controlling how office buildings shape up differ from county to county, but buildings are required to meet local regulations on height, traffic and parking, and, to varying degrees, design.

While signature buildings have cropped up all over the Washington area, some say the phenomenon has occurred with a particular intensity in Northern Virginia, especially in Fairfax County.

A tradition of free-for-all, private-sector development contributes to the proliferation of signature buildings in Northern Virginia, in contrast to a history of more government involvement in the development process in some Maryland suburbs, according to architect Robert L. Miller, who is president of a Washington public relations firm that works with architectural and engineering companies.

Others believe the concentration of such buildings in Fairfax stems from a perception in the marketplace that Northern Virginia is the hot place to be.

"Northern Virginia, for whatever reason, currently has been defined as a pretty good address; Montgomery County, too, and Prince George's County less so," said Frank Spink, director of nonresidential research for the Urban Land Institute. "When a developer looks for a site, he is going to tend to look for a good address."

Increasingly, as higher-rent businesses are drawn to the suburbs, speculative or no-ownership buildings are being constructed without having been leased first, Spink said. It is frequently these buildings that have taken on the inventive, billboard-like approach, he said, as a way to attract publicity -- and tenants.

Spink and others cite the clusters of concrete, steel and glass that make up Tysons Corner as a vivid example. In little more than two decades, the area has been transformed from a country crossroads to an emerging city with more office space than downtown Miami.

Like dozens of carolers singing different choruses, buildings of all shapes and sizes have shot up at Tysons. Many have taken on nicknames recognized by government officials and citizenry alike.

"It's really a city that has reverted to a medieval way of life," Miller said. "It's all private property. Each one of these places is its own little fortress. There's very little that's sort of a civic environment, like a park, a statue, a public market."

In some cases, the results have prompted cries of dismay from observers of the development scene.

"There's a huge problem with restraint," said Sherwin Greene, a professor of urban and regional planning at George Washington University. "I get concerned because we all have to look at it. On a lot of them, it's not clear exactly what they're doing."

Even some Fairfax officials seem to have concerns about the appearance of Tysons Corner.

"It's a little too late for the urban design element to get in," said Sheng-Jieh Leu, senior urban designer for the county's Office of Comprehensive Planning.

It is in Tysons Corner that one finds the mirrored, cube-shaped Tysons Office Center at Rte. 7 and Gallows Road that has been dubbed "the flash cube building." The description "never fails to get people here. It's a pretty good landmark," said Dick White, president of the eastern division of the Benham Group, the national architectural firm that designed the six-year-old building.

Also here is the headquarters of the National Automobile Dealers Association, housed in an 11-year-old building with three concrete silos affixed to its side at Westpark Drive and Rte. 7. The building, designed by the Alexandria-based architectural firm of Vosbeck, Vosbeck, Kendrick & Redinger, prompts questions from visitors who wonder whether cars or missiles are stored inside, said one receptionist.

And it is in Tysons Corner that a soaring salmon-colored, limestone building of arches and columns has been added to the skyline. The building is the massive JTL Tycon Towers I, the first of three identical towers being developed by James T. Lewis at the Capital Beltway and Rte. 7.

To some, it resembles a shopping bag with handles. For many, it defies an easy definition.

"You're overwhelmed by that thing on the Beltway, for no purpose," said Edmond F. Rovner, an aide to Montgomery County Executive Sidney Kramer. "You just say, 'Oh my God, what is that? Why would you do that?' . . . . This thing seems to be an obstacle course for birds."

The chairman of the Fairfax County Architectural Review Board shares that sentiment. Susan Notkins said she is convinced that renowned architect Philip Johnson, who designed Tycon Towers, played a joke on his client and the public.

But Lewis almost swells with pride when he talks about his project, which will cost $250 million to $300 million when complete.

The first tenant moved in last December, and so far, 45 percent of the office space in the first tower has been snared by lawyers, real estate developers, communications groups and consultants who have paid above-market rates of $24.50 to $28.50 per square foot, according to the leasing agent.

"I think it's magnificent," Lewis said of the project. "It provides a touch of great architecture for the area."

Lewis, who also is developing the $1 billion PortAmerica project in Prince George's County, dismisses the less than charitable comments about his works. "It's the responsibility of a developer to make an attempt to do something nice," he said.

The six-story Tycon Courthouse, a k a "the toilet seat building," at Rte. 123 and Old Courthouse Road, is also a Lewis project. It was designed by architects Volker Zinser and Barry Dunn, who work in the building.

Zinser said the inspiration came while he was reading a book about two 19th century French architects who designed large-scale projects that explored geometric volumes. He said he doesn't mind that people describe the building as a toilet seat -- he said he has heard it called "nastier names."

"What's important about that is simply the fact that it has risen out of anonymity," he said. The structure, which includes 450,000 square feet of office and retail space, is 89 percent leased, according to leasing agent Mike Shuler.

To the east, visible from Rte. 50 and the Beltway in Prince George's, the Metroplex II office building has much the same effect. It is an intriguing 13-story building made of dark solar-gray glass and precast concrete.

Arthur Cotton Moore, the architect who designed it and a number of other distinctive projects, including Washington Harbour and the Old Post Office Pavilion in the District, thinks Metroplex II evokes a romantic imagery.

He likens it to an archeological ruin, because of its columns and resemblance to an eroded square on the entrance side. But others who work there or pass it have a different opinion.

"This is the 'Darth Vader building,' " said Robert Liguori, a producer who works for the Discovery Channel, a cable television network that has offices in Metroplex II. "It's large. It's black. It has that evil type of look to it.

"I'll start to tell people where I work and they say, 'Oh yeah, that's the Darth Vader building.' "

Alan Feinberg, a principal urban designer for Prince George's at the Maryland-National Capital Park and Planning Commission, said, "I've never heard it called anything else."

When told of the menacing description of Metroplex II, Moore said he was "shocked . . . That's out of the blue."

Like some other members in the development community, Moore said he is troubled by what he sees on the horizon in the Washington suburbs. "Tysons Corner is probably the worst example," he said. "It is so disconnected. There's no glue to weave it all together . . . . It's a problem in most suburban areas; it's a problem all over America."

But not all buildings shaping the suburban skyline are shouting statements. Some are getting their message across in quieter ways.

A much-praised example is Fair Lakes One. The chevron-shaped office building with four stories of mirrored glass reflects the woodsy environment of the 620-acre Fair Lakes office park at I-66 and Rte. 50.

The 130,000-square-foot building recently won an award for excellence from the American Institute of Architects' Northern Virginia chapter, and top honors in Fairfax County's third annual exceptional-design awards program.

The architectural firm of Davis and Carter, and developer Hazel/Peterson Cos., shared the awards for Fair Lakes One.

"It makes a strong statement, but in my judgment it makes a strong statement because it fits so well into the natural environment," said James Todd, president of Hazel/Peterson Cos.