At Tysons Corner, the fall sales are in full swing. There are Cuisinarts at Bloomingdales, Persian rugs at Hechts and fashionable twill shirts at Woodies.

Elsewhere in the complex are the latest offerings in how to combat urban terrorism, how to plan a computer wargame, and how to neutralize electronics eavesdropping.

These services - and many others equally exotic - are among the offerings of a less-known but growing group of merchants who are calling the burgeoning Tysons Corner complex in Fairfax County their home.

Called "the Beltway bandits" by some, these merchants are government consultants. According to one estimate, there are now 350 of them, mostly at Tysons but also in offices that border Rte. 495 into Montgomery County.

Much of what these consultants do for U.S. taxpayers is shrouded in secrecy in the concrete and tinted glass office towers of the Beltway.

"People don't say anything because it's just better not to talk" says David Pogue, a public relations consultant to several Beltway entrepeneurs. Pogue attributes the secrecy to the fact that much of the work is for the Defense Department, which insists on keeping it classified.

Even so, there are occasional disclosures of the consultants' more exotic work - disclosures that many say are natural in any industry the size of consulting. For instance, the non-profit Mitre Co. has become Fairfax County's largest private employer, with 1,000 workers who runs 250 projects for the federal government.

Last year alone the Mitre Projects at Tysons brought in $42 million and included a wide range of contracts.

Mitre workers compared various solar energy projects for the Department of Energy, advised NATO officials on whether their communications gear could survive a nuclear attack and helped the Pentagon on another communications project called "C-3."

Despite current efforts by the Carter administration to curb the use of consultants, they seem to be flourishing. They are one reason that Fairfax County industry hunters last week bragged that the amount of commercial office space in the Tysons complex soon will be doubled by new office construction.

Tysons, the county's economic development authority said, soon "will have its own 'skyline'" of high-rise buildings.

"If there was no (federal) research being done, it would probably wipe out Tysons Corner," said David Edwards, head of the development authority.

In a survey last year Fairfax County found that the number of research firms in the county has more than doubled in the past seven years, to a total or more than 17,000 workers. Most of the firms are located in the office building and office parks around the Tysons Corner Shopping Mall.

There also is a string of consulting firms located along Interstate Rte. 270 in Montgomery County an area where many consultants settled before development of the Tysosn complex began developing more than 15 years ago.

Tysons has a special allure for the consultants. "They have good access to Dulles," notes Robert Torgerson, a spokesman for the county economic development authority. "And you can get into the city and get your money (easily). And part of the name of the game is to get your bucks."

That's the reason that the use of consultants is troubling the Carter administration. "They are called the Beltway Bandits because they seem to ride in and out of government so often, looking for contracts," said Lester A. Fettig, an official of the Office of Management and Budget.

The precise flow of dollars from Washington to the Beltway is hard to pin down. Last year OMB surveyed 64 government agencies and discovered about 34,000 consulting contracts totaling $1.8 billion. This year the figure should be lower, although well in excess of $1 billion, an OMB official said.

"Without question, we have the largest concentration of consultants here," said OMB's Fettig. Large portions of the government's consulting money also goes to Southern California and to Boston where consulting firms clustered in one area are know as the "Route 128 Bandits."

"I suppose if we have been near the Rock Creek Parkway, we would have been known as the Rock Creek Robbers," said Earle C. Williams, president of Tysons-based BDM Corp., whose staff recently completed a study for the Nuclear Regulatory Commission dangers terrorists could pose to nuclear reactors.

Within the consulting community all is not harmony. THere is a sharp rivalry between profit-making and nonprofit consultants at Tysons - a division that was probably widened this year by an OMB directive that exempted the nonprofit firms like Mitra from a rule requiring competitive bids for government contracts.