Discovery Communications has agreed to lease the former Caldor building in downtown Silver Spring, significantly broadening its commitment to Montgomery County's most ambitious redevelopment project.

The fast-growing media company already plans to build a 600,000-square-foot headquarters within the Silver Spring redevelopment district, the centerpiece county officials hope will lure more film and production companies to the neighborhood.

Now Discovery has given new momentum to that vision by signing a 15-year lease to occupy a vacant 150,000-square-foot building that has proved very difficult to rent since Caldor left.

Discovery will use the almost entirely windowless building, located across East West Highway from its planned headquarters, to house its vast computer system, tape library, editing center and other production equipment. Some of the 400 employees expected to work at Discovery's Creative and Technology Center are due to begin moving in next April. Company officials say the lease and renovations are worth about $25 million.

"This site gave us a great opportunity to consolidate our operations and to have room to grow," said Pandit Wright, Discovery's senior vice president for human resources and administration. "We are making a total commitment to Silver Spring as a neighborhood."

County officials and neighborhood activists had worried about the fate of the Caldor building since the discount chain pulled out of the Washington market last year amid financial troubles. Its size and bunkerlike design posed severe problems for leasing agents working in a neighborhood that has seen several economic development efforts rise and fall over the last decade. Many were afraid that an empty Caldor site could scare off other companies considering a move to Silver Spring.

"In the past, when companies went out of business, the storefronts stood vacant for years, and we had to move heaven and earth to find someone to use them," said County Council member Derick Berlage (D-Silver Spring). "This is a sign of the renewed strength of Silver Spring."

Discovery has grown so rapidly in recent years that it occupies at least six different buildings at its current base in Bethesda. The company is the world's largest producer of documentary films, many of which it shows on the Discovery Channel. Company officials said that as many as 1,800 employees could work at the headquarters and former Caldor site when their move to Silver Spring is complete in 2002.

Wright said the company was planning on including space for its computer systems and production work in the headquarters building. But she said that by leasing the Caldor site, the company will have even more space available for expansion.

The Discovery lease propels efforts to revitalize the 300-acre Silver Spring redevelopment district in two ways. First, it lowers the rental vacancy rate, lifting the value of nearby rental properties. Second, it gives a push to redevelopment efforts in southern Silver Spring as the $321 million town center-style project gets going in the business district's northern section.

Hoping to capitalize on Discovery's lease, Montgomery County Executive Douglas M. Duncan (D) plans to step up street-cleaning crews, neighborhood police patrols, facade improvement grants and other revitalization programs in the area; so far, they have been focused farther north. He plans to create a South Silver Spring Arts and Technology District, mostly to market the area to media and creative arts companies.

"The Caldor deal has been absolutely instrumental in making these activities come to life," said Lori Gillen, director of the Silver Spring Regional Center, the county agency leading the redevelopment efforts. "This, in my opinion, has been the one thing that legitimately allows us to call it an arts and technology area."