Fairfax County, attempting to preserve the value of its recently awarded cable television monopoly, has ordered a small subscription television company to dig its cables out of the ground in a subdivision near Fort Belvoir or face a lawsuit next month.

County Executive J. Hamilton Lambert sent an ultimatum to Skyvision Corp. last week, following up on earlier warnings that ordered the Landover-based company to remove the cables it has just installed in the Sequoyah community of 1,018 town houses and apartments.

The letter reflects a recent trend in the high-stakes pay television industry that poses serious problems for major cable operators and local governments. Fairfax officials, like those in Prince George's County and elsewhere, fear that small, unregulated companies that pull in TV programs from earth satellites by using large antennas will raid the county for the most lucrative and easily serviced apartment complexes and subdivisions before county-approved cable firms can build their systems.

Such raids would both reduce the taxes the county collects, the officials said, and leave many county residents with inferior service.

"It would appear there's a rush to beat the operator into these subdivisions, and it's possible that as a result, the consumer's going to be shortchanged," an aide to Lambert said yesterday.

Officials at Skyvision were unavailable for comment yesterday. County officials said Skyvision has said it is not a conventional cable television company and so cannot be regulated by the county.

The Fairfax Board of Supervisors, after years of study and debate, last month agreed to give Media General Cable of Fairfax County Inc. a 15-year cable franchise in the wealthy suburban county.

Media General, the local subsidiary of a giant communications company that owns the Richmond daily newspapers, in turn promised to build an $85 million system offering more than 100 channels, provide two-way communication and allow community groups to produce and televise their own programs.

During the long wait for cable service, however, many apartment complexes inside the Capital Beltway have signed contracts with companies like Skyvision, which usually build a satellite receiving dish on the roof and offer a handful of sports, news and movie channels to residents. Unlike Media General, such companies do not have to pay 5 percent of their gross revenues to the county and do not have to offer public access or two-way television.

"They of course are not playing on the same regulatory playing field as the cable operators, and yet they dance in and take away some of the choicest parts of the county," said Ed Dooley, vice president for public affairs for the National Cable Television Association.

The small satellite companies have proliferated since the federal government deregulated the business in late 1979, and local governments' right to regulate the firms along with major cable systems is just beginning to be tested in court. Fairfax stepped into the Sequoyah situation after county officials said they saw cables being laid without county permission under public streets owned by the county. Skyvision officials could respond by challenging the county-granted cable monopoly under federal antitrust laws, officials said.

A resident of Sequoyah said yesterday Skyvision promised six channels for about $15 per month, with no installation charge and service scheduled to start next week. "I would guess the major selling point they have with customers is, 'entertainment now,' " a county official said.