A motorist driving by the squat, unmarked beige building along Nokes Boulevard in Sterling might not give the generic structure a second look. It could be any warehouse, in any suburb.

But its blandness is deceptive--and intentional.

The two-story warehouse, with blackened windows and a cinder-block wall an inch behind the glass, holds inventory deemed valuable enough to warrant constructing it with reinforced concrete capable of withstanding car-bomb attacks and AK-47 gunfire.

It is in this fortress, along with dozens like it in the Washington area and countless others around the country, that agents of the Internet economy are protecting the world's most valuable asset: information. The structures house hundreds of computers--servers, actually--where World Wide Web sites live.

This particular building north of Dulles International Airport is owned by Exodus Communications Inc. of Santa Clara, Calif., one of the biggest players in the Web hosting industry. Hosting the Web sites of Corporate America is a pronounced growth industry in the burgeoning world of electronic commerce--a $770 million business last year that Internet analysts estimate will grow to nearly $12 billion by 2002.

The facilities are scattered at sites in major metropolitan areas throughout the world, with more than three dozen of the virtual warehouses for the information age in the Washington area, particularly in western Fairfax and eastern Loudoun counties in the midst of the high-tech corridor along the Dulles Toll Road.

One of the prime reasons for the proliferation of data centers here is the enormous amount of fiber-optic cable in the ground, making it easy to connect to the Internet backbone. About 60 percent of the world's Internet traffic goes through Northern Virginia.

As recently as 1995 the Web hosting industry did not exist. But a handful of start-up firms correctly perceived that most corporations eventually would not have the technical expertise, the capital resources or the desire to house and operate their Web sites by themselves and successfully keep them on the Internet 24 hours a day, seven days a week, 365 days a year.

That's where such Web hosters as Exodus and Global Crossing Ltd., based in Hamilton, Bermuda, stepped into the breach as outsourcing operations, much the way an outside firm might take over a company's payroll chores.

Now, numerous other firms, including such giants of the technology and telecommunications world as Intel Corp., PSINet Inc., AT&T Corp., America Online Inc., GTE Corp. and MCI WorldCom Inc., also have decided that there's money to be made in hosting other corporations' Web sites.

"The demand for Web hosting is huge and is going to go through the roof," said Bill Whyman, an Internet strategist for an arm of the stock brokerage Legg Mason Wood Walker Inc. of Baltimore.

In just the last few days, Equinix Inc. of Redwood City, Calif., announced an alliance with Bechtel Corp., the worldwide construction giant, to spend $1.2 billion to build more than 30 new hosting sites in the next four years, while Cable & Wireless Inc. of Vienna said it would spend $500 million to build eight more centers, including one in Reston.

For the communities in which they are located, data centers seem to be ideal corporate citizens. Large capital investments, sometimes as much as $900 a square foot above the cost of real estate, generate relatively high real estate taxes. And, because the staffs needed to monitor the facilities are small, the companies do not burden already crowded roads and schools.

But as communities rush to market themselves to these Web hosters, the real estate and development worlds have had to scramble to keep up.

"Let me tell you, [this] caught the development community completely off guard," said John McEvilly of Millennium Realty Advisors in McLean. "Nobody had the kind of buildings up and ready for these guys when they started kicking around in the market earlier this year."

The types of buildings best suited to Web hosters' needs are industrial structures, which are not common in the Washington area. "We're such a white-collar, clean marketplace here that nobody has had a requirement of that kind" in a long time, McEvilly said.

For example, he said, the floors in these centers must be able to withstand at least 200 pounds of weight per square foot--twice that of floors found in typical commercial structures.

Locally, Doug Humphrey, founder of the Internet service provider Digex Inc. and, more recently, SkyCache Inc., a satellite Internet broadcasting company, has teamed up with several other Washington area entrepreneurs, including developer Fred Ezra and the Carlyle Group, to start Core Location. The new firm hopes to transform old buildings into Web-hosting sites.

Netscape Communications Corp. founder Marc Andreessen also is entering the industry through his new venture, Loudcloud Inc., based in Menlo Park, Calif. Loudcloud will operate data centers and provide other services to start-up companies.

At the moment, there seems to be a long line of companies wanting to lease space in the data centers.

Steve Danker, vice president and chief information officer for Musicland Stores Corp., the corporate parent for the chain of Sam Goody music stores, said that after an extensive search his firm recently hired Global Crossing.

Inside, the Web hosting sites, through which millions of Internet connections are routed each day, are extraordinarily simple-looking: stack after stack of computer gear. There may be network servers, or routers, or hubs or data switches or load-balancing equipment, depending on the company. Some of the companies have boldly labeled their equipment with their corporate logos, while others have sworn their Web hosters to secrecy.

The facilities typically have security worthy of the Central Intelligence Agency, to prevent unwanted intrusions.

When a company places its network servers at a data center, it is essentially turning over the very guts of its corporation. Banks, Internet service providers, long-distance telephone companies and even governments store critical information on these computers, and every day the machines handle millions of transactions.

As Joseph T. Balsamello, a Global Crossing vice president, put it, "These are the sites the government believes terrorists will go after."

With that in mind, the facilities do not call attention to themselves. Neither Exodus nor Global Crossing has any corporate signs on its facilities in Northern Virginia, leaving passersby to think they might be an office building or storage depot. Exodus does have a floor mat outside the front door at its Nokes Boulevard facility. But no one can get into either facility without a corporate laser-scanned entry card or if a guard electronically unlatches the door.

Equinix, which spends between $1 million and $5 million on upfront security costs at its sites, requires visitors to pass an electronic palm reader of sorts that has "learned" to recognize the hands of people authorized to enter the building.

Once past spartan lobbies, visitors typically have to be accompanied through "man-traps," small hallways closed off by a secure door on each end, by company officials.

Or, if they're company employees or authorized construction workers, they have to again display their electronic card or have their finger or palm prints read on a hand scanner after they've entered a personal identification number. Similar security is in force throughout other portions of the facilities.

Security cameras are everywhere. As Balsamello said, "You can't do a thing in that data center without us watching you."

At Exodus, openings that look like darkened windows are dark for a good reason--there's a cinder-block wall an inch behind the glass--and the lobby walls are laced with bulletproof Kevlar.

Local officials, even though they're mindful of the Web hosters' security needs, typically insist on the false windows for aesthetic reasons. As Herndon zoning administrator Lisa Gilleran said, "You don't want a building that looks like a bunker."

Companies take all sorts of things into consideration when planning a data-center site. Jay Adelson, chief technical officer and a co-founder of Equinix, said some Web hosters prefer to be under airline flight paths, on the theory that air traffic controllers would know when a terrorist had entered the airspace. Other firms prefer the opposite, thinking it will limit the chance that a plane might crash into their building. He declined to say which way Equinix has come down on the issue.

Some of the racks of computer equipment in the data centers are in common areas shared by several companies, while others are securely locked behind black wire fences or even secured in bulletproof enclosures.

System failure is not an option, and Web hosters like to tout their redundant power sources.

At the Equinix site in Loudoun County, for example, most equipment is connected to two separate power sources. There is also a backup generator. In the unlikely event that all normal power supplies dry up, there is a battery pack the size of car in the middle of the electrical room with enough juice to power the building--which uses three times as much electricity as a typical office building its size--for an entire day.

As Internet strategist Whyman said, "If someone comes in and puts a baseball bat to your server, you're out of business. If you took out Exodus, it would wipe out 26 of the top 100 content providers" on the Internet. (Most customers of data centers scatter equipment at various centers to protect against a shutdown at any one site).

Such security is not cheap. Exodus said each of its 1,745 customers typically pay $176,000 annually to have the firm manage their Web sites.

Despite such costs, Mario Morino, who owns a Reston office building that serves as a home for 18 start-up technology firms, said he believes more companies will hire other firms to host their Web sites.

"When new technology comes, it drives people to do it themselves," he said. "They come to realize all the backup costs, employees and more. It appears it gets cheaper till you add it all up."

CAPTION: Network technician Chris Murray keeps an eye on things at Global Crossing's Web hosting facility in an anonymous building in Herndon.

CAPTION: Network technicians keep watch on operations at the Web hosting facility that Bermuda-based Global Crossing Ltd. operates in Herndon.