When told about the recent grand opening of the Greenbelt Hilton Hotel and Towers, a colleague asked incredulously, "A Hilton hotel in Prince George's County?"

When told that the $30 million property is an 18-story hotel with luxury suites comparable to some of the better accommodations downtown, the same colleague reacted as one might upon being told that Bloomingdale's was going to open a store in Anacostia.

Her reaction was no more incredulous than those expressed by many of the 2,000 or more invited guests who spent the evening at the new Hilton, sampling the likes of oysters on the half shell, caviar and champagne.

The Greenbelt Hilton is one of at least four hotels to open in Prince George's County within the past year and, at least 10 more, including the first of the Marriott Corp.'s Courtyard group slated for the Washington area, are either under construction or proposed. Ten years ago, there probably were fewer than six reputable chain motels in the entire county. The recent boom in new hotel construction and expansion in Prince George's County is expected to add about 2,000 rooms to the existing inventory.

To be sure, Prince George's County hasn't suddenly become a tourist mecca. The apparent demand for more and better hotel accommodations is tied directly to the county's emergence as an integral part of the Washington area's economic boom. Economic development, driven by explosive growth in commercial construction over the past three years, has radically changed the landscape as well as the personality of Prince George's County.

Nonetheless, the county's image has changed little, if any, in the minds of many in the region. The mythical Prince George's County remains saturated with low-density commercial sprawl mainly consisting of warehouses, look-alike garden apartments, garages and -- beyond the Capital Beltway -- farmland and rural villages.

The real Prince George's County is a hotbed of economic development. The county's Economic Development Corp. reports there are 200 major commercial projects in various phases of development or planning. Nearly half of those are office or industrial parks. Development planned during the current year includes about 2 million square feet of commercial office space and facilities for companies engaged in high technology and research and development.

Major regional, national and international companies have heeded the economic development coporation's call to "Follow success to Prince George's County." Among major local companies that have their headquarters in the county are Giant Food Inc., Dart Drug Inc., Hechinger Co., Trak Auto Corp. and Crown Books Corp. A new joint venture by RCA and Hughes Aircraft recently was added to a long list of major corporate tenants that include Martin-Marietta Corp., Computer Sciences Corp., Litton Industries, Control Data Corp. and HRB-Singer.

The county's sales pitch is hard to ignore. It has the cheapest and largest inventory of undeveloped land in all of metropolitan Washington. Approximately 1,200 acres of developable or underdeveloped land are located in close proximity to Metro stations in the county. Prime office space in the heart of the county's major commercial sector can be leased for a mere $15 to $18 a square foot. Comparable space costs between $19 and $25 a square foot in Tysons Corner, $23 to $30 in Bethesda, $15 to $20 in the Reston-Herndon area and $25 to $36 in Washington's central business district.

Located in the heart of the Baltimore-Washington corridor, Prince George's County has the best road network in the region. About 40 percent of the Capital Beltway runs through the county.

The latest available figures show that the county has a median household income of more than $32,000 and an unemployment rate of around 3 percent, among the lowest in the area.

Selling the county to some potential office users and homeowners in the Washington area remains, difficult, nevertheless. Developers, on the other hand, see a bonanza. They're planning more office parks, a 50-story office tower and world trade center, more hotels, and waterfront villas costing $250,000 and up.

Still, there is a 13-percent office vacancy rate in the county, admittedly a concern among economic development officials. Perception of the county remains a serious problem locally, they acknowledge.

Prince George's County is "primed for upscale development," the development corporation noted in the latest edition of its newsletter. That was the message to several developers, financiers and other business leaders at a recent seminar that was sponsored by the Washington law firm of Linowes & Blocher.

For those who attended the seminar and for those who ventured out onto the Beltway to the Greenbelt Hilton, the signs of upscale development were clear. It will take a hard sell to persuade the nonbelievers. Perceptions change slowly in the abstract.