More than 4,300 hotel rooms are being built or planned in Fairfax County, according to a report by the county's Economic Development Authority.

The 18 new hotels or expansions of existing facilities included in the report are spread throughout the county, but are concentrated in the Tysons Corner area.

The building surge in hotel rooms follows the county's continuing boom in industrial and commercial development, which hit an all-time high of $399 million in fiscal 1984.

Although the number of rooms under construction or planned seems high, Fairfax officials said they think the market can absorb the new facilities.

The current level of construction surprised some people, however, according to Donna Osborn, a member of the Economic Development Authority staff who was responsible for preparing the report. "There has been such a need for the facilities in the past, and those needs have certainly been intensified by the county's rapid growth," Osborn said.

In addition to the hotels that showed up in the report, several others are being planned. For example, a Fairfax development company is asking the county to change its land-use plan to allow construction of a hotel adjacent to Fairfax Hospital. Another half-dozen hotels have been discussed in proposals for changing the county plan. Another developer said this week that his company is looking at four sites for hotels. In addition, the hotel survey does not include the second of two hotel facilities that will be built at Tysons II.

The facilities under construction spread from Dulles Airport to Springfield and represent a cross section of the types of hotels being built across the nation.

Hotels are being built for the budget-minded client and for those with a lot of money to spend. The facilities are being designed to accommodate the needs of different clientele by providing special spaces for business travelers who will be staying for several days, as well as just overnight.

For example, Holiday Inn has opened its Embassy Suites hotel in the Tysons Corner area. It offers "the corporate traveler a suite complete with living area, bedroom and bath," according to the report. Nearby, the same company is renovating an older traditional motel-style facility adjacent to the giant Tysons II mixed-use project now under construction.

"Increased office and industrial activity and the accompanying surge of hotel construction has forced diversification," the report said.

"The Northern Virginia hotel market, as measured by rates and occupancy, is the strongest in the Washington metro area," said W. Wesley Ayre of Laventhol & Horwath, an accounting firm that monitors hotel occupancy rates and trends in the Washington area.

Ayre, who said he was aware of potential hotels not listed in the development authority's report, said the market would be "soft" if all the rooms were completed and hit the market at the same time. But he said that he doesn't expect that to happen.

Even if a soft market developed, that would not necessarily mean any individual hotel would be in trouble, he said. "There is no question that an individual hotel can do well in a soft market," he added.

Pat Hannum, director of real estate and information resources for the development authority, and county officials agreed that Fairfax has several hotel submarkets, including Tysons Corner, Washington-Dulles International Airport, the Reston area and the Springfield area; hotels in those particular areas are expected to compete with each other, rather than with hotels in other parts of the county.

Meanwhile, several hotel chains, including Marriott and Holiday Inn, are reportedly looking at Fairfax with specific plans in mind, but no specific locations.