Complete corporate relocation is a rarity, said Bud Eaton, director of the Office of Economic Development for Montgomery County. Thus, when Lightnet, a fiber-optics communications company in Connecticut, relocated to Jefferson Plaza in Rockville, the development office was delighted.

"They add to the strengths of the county," said Eaton, who says his office is cultivating such firms for the so-called "Satellite Alley" along Interstate 270.

Lightnet, founded in 1983, decided to move to the Washington area because many of its clients, common carriers such as U.S. Telecom and RCA Americom, are here. However, the selection of Montgomery County was based on two factors: It was convenient for employes already working in the area, and officials liked the building and its amenities.

Jefferson Plaza I, a 120,000-square-foot building curved like a teardrop, has a split-level granite lobby. When Building II is completed, the structures will share a small park with two 15-feet waterfalls. The total size of the project is 500,000 square feet. Building I is 75 percent leased.

The buildings' developer, Baier Properties Inc., a Rockville investment building firm, also is building properties in Fairfax County. Lightnet has a 10-year lease, valued in excess of $10 million, with options for additional space.

In other developments in commercial realty:

CACI Inc., a professional and high-technology service corporation, leased 95,000 square feet at Willow Oaks Corporate Center in Fairfax from The Prudential.

The American Postal Workers Union leased 42,148 square feet at 1300 L St. from Lehrco Corp.

Giant Food Inc. leased 55,330 square feet at Leisureworld Plaza in Silver Spring from Rossmoor-IDI Commercial Center Associates.