E-Systems Inc., a major defense contractor, plans to nearly double the size of its electronic warfare division in Northern Virginia over the next few years and is expanding into a second facility in Fairfax in February.

The Dallas-based high-technology firm has leased a three-story, 200,000-square-foot building in the High Ridge Corporate Office Park in Fairfax for its Melpar Division, which also will remain at a 300,000-square-foot facility in Falls Church.

The division, whose main customer is the Defense Department, makes remote-controlled reconnaissance systems, combat radios and other electronic warfare devices. E-Systems Inc. is a Fortune 500 company with sales last year of more than $6 million, a spokeswoman said.

Melpar employs 1,100 persons in this area and plans to hire another 850 by the time it has occupied all of its new space, probably in about two years, according to Ira Apter, Melpar vice president for operations.

The firm will add about 200 persons to its operations in February, when it will start to move into the new building. The second stage of the expansion is likely to take place in October or November next year, and another 200 to 250 persons will be hired by the end of 1982, Apter said. It probably will take another year or more after that to finish the move and to hire the rest of the planned staff additions, he added.

Melpar, whose main customer is the Pentagon, is one of the largest electronic warfare firms in the country, another company spokesman said.

John W. Dixon, chairman and president of E-Systems, said in a statement that Melpar's recent growth has made it one of the company's key operations.

"The new facility gives us access to a larger labor market, and we need the space to support additional engineering development," said Talbot Huff, vice president and general manager for Melpar.

A spokeswoman for Julian J. Studley Inc., the brokers in the leasing transaction, said the move makes Melpar one of the first companies to locate in the westernmost part of Fairfax County.

Westinghouse Electric Corp., meanwhile, announced that in January it will establish a new product development center in western Fairfax that will employ 80 persons within the next three years.

The center will be housed in a 17,000-square-foot building in the Fairfax Executive Park and will serve as a central engineering base for development of electromechanical products used by industry for controlling electric motors, the company said.