Cellular telephone service has made its debut on Maryland's Eastern Shore and is about to be activated in rural Virginia counties near the Washington area and in a part of rural West Virginia.

Bell Atlantic Mobile Systems is operating the Eastern Shore system in an area of about 2,000 square miles, including Ocean City. In recent weeks it has turned on four transmitter-receiver stations.

Cellular One, the Washington area's other cellular company, will be the operator for areas in Virginia and West Virginia. It plans to begin phasing in service in its 11,000-mile franchise early next year, with service available everywhere by the end of the year.

Herschel Shosteck Associates Ltd., a Silver Spring research firm that follows the cellular markets, estimates that the two companies have about 220,000 subscribers in the Washington-Baltimore service area. Growth has been slowing recently, the research firm said.

The new zones represent untapped new markets. Cellular One's contains about 750,000 people, while Bell Atlantic Mobile Systems' has 331,000. Business can come both through local people signing up and subscribers from other areas whose use the service while driving through.

Cellular One's new areas will include the regions around Front Royal and Winchester; Fredericksburg and Culpeper; Virginia's Eastern Shore; and Martinsburg in West Virginia.

Major American cities began getting cellular service in the early 1980s. In a series of lotteries in recent years, the Federal Communications Commission has awarded rights to operate the service in unserved rural areas.

Many companies that win the lotteries sell the rights to other companies, which build the systems. This is how Cellular One got its new areas. Bell Atlantic Mobile Systems, however, won its new license directly from the FCC.