When a new concrete and glass high-rise office tower officially opens its doors in Silver Spring next month, tenants on one side of the building will look down on the decaying central business district of Colesville Road, while those on the other side will have a panoramic view of the sleek, elevated Metro rail station, which is both the hope and disappointment of the sagging downtown of the aging suburb.

Metro had been expected to herald the salvation of downtown Silver Spring, a once-fashionable business district of wide avenues and airy department stores that fell victim to the car and the modern shopping mall. When the first train breezed into the Red Line station in 1978, it was hoped that business development and revitalization would follow.

But four years later, Silver Spring's latest hope is a building--the first new office structure there in 10 years--at 1100 Wayne Ave. Developed by Lloyd W. Moore, the $16 million complex on the site of the old Pumphrey funeral home boasts 134,000 square feet of office space and a glassed-in mezzanine with retail shops and a fountain.

Silver Spring's boosters, who once pinned their hopes for a revival on Metro, now are looking to "1100 Wayne Avenue" as the area's salvation, the long-awaited spark that will ignite an economic development boom.

But after the disappointment that followed Metro's opening, the predictions are more tempered.

"I don't think it's completely taken off yet," said William Barron, a planner with the Maryland National Capital Park and Planning Commission. "But adding anything there is positive. The last major building to go up in Silver Spring was in 1972. So Lloyd's office building will certainly help."

The optimism was boosted by Moore's announcement last Monday that 40 percent of the new building has been leased to the American Bell Incorporated subsidiary of AT&T, belying the development community's fears that that office space in Silver Spring is not marketable.

The announcement of the AT&T lease was enough to prompt a press conference on the steps of 1100 Wayne, at which Montgomery County Executive Charles W. Gilchrist heralded Silver Spring's "transformation into an exciting and vital urban environment, which is once again attracting quality new development."

The hope now is that developers will look at Moore's success in finding a major tenant and decide that Silver Spring is indeed a prime site for private capital investment.

But not everyone is convinced.

"We aren't beginning any projects in Silver Spring and we're watching the market very carefully," said Oliver T. Carr, one of this area's principal developers. "Right now, we think it looks very weak . . . . It just seems the major thrust today in the whole metropolitan area is Northern Virginia."

That could change, Carr said, as rising costs elsewhere make Silver Spring "terribly attractive."

Silver Spring has definite selling points, which developers emphasize when searching out potential tenants and which county officials use in searching for investors. Besides lower rents, downtown Silver Spring is only a mile from the Beltway, with easy access to Baltimore, putting tenants in reach of two regional markets. And the Metro puts downtown Washington just a Farecard away.

But economic development, like the stock market, is partly a game of psychology -- and for a long time the belief was that nothing was happening in Silver Spring. "It's an image problem," said David Richards, project manager for the Oliver T. Carr development company. "Its image was of being stagnant. I think now, with Lloyd Moore's project, Silver Spring can quickly turn that around."

Richards is watching the Silver Spring market and tracking the success of Moore's efforts, since his company is considering a major project of its own: an office and retail store complex at Colesville Road and East-West Highway.

Richards allegedly is testing the waters for potential tenants, to see if there is enough interest in such a project. But Carr has cautioned that so far "our view really has not changed" about Silver Spring being a weak market.

Five other projects already have been approved by the planning commission, including another Lloyd Moore development at 8484 Georgia Ave. that is scheduled to break ground this spring. That building will add another 143,000 square feet of office space.

Other buildings include a new Silver Spring Business Center at Colesville and Roeder Roads, the Silver Spring Metro Plaza, Gateway Building and Silver Spring Center.

Those projects--coupled with the county's $30 million investment for new street lighting, road repair and median strips on Georgia Avenue -- substantially will alter the streetscape of the area's oldest suburban downtown, which in the days after World War II developed from the wilderness estate of Francis Preston Blair into the Washington area's retail and commercial center.

In those heady building-boom days, Silver Spring was where development was happening, where metered street parking made its debut in 1945 and where Hecht's opened its first suburban store.

Silver Spring's decline came as quickly, with the opening of the Capital Beltway in the late l960s, and the growth of the suburban shopping malls that made its once-fashionable shopping district obselete. A sewer moratorium in the 1970s blocked all new development, and the area lost 21 percent of its population between 1970 and 1980, according to Gilchrist.

Metro's opening was not enough to reverse years of decline. Geographically, the Metro station was an unlikely spark to revive the business district, since the station is somewhat isolated from the Colesville Road and Georgia Avenue intersection. "You really have to go out of your way to get to a store from the station," Barron said.

And, unlike the planned Bethesda Metro station at Wisconsin Avenue and Old Georgetown Road, no development was planned immediately around the station itself.

"We always thought the opening of the Metro station would bring change," said local lawyer James W. Tavel, the former Chamber of Commerce president. "But we never thought it was going to bring wonderful, immediate change overnight."

"All that Silver Spring needs is a spark," said Richards of the Carr Co. "And 1100 Wayne may be that spark. It needs that major injection of development activity -- cranes in the sky -- to get more developers bullish on Silver Spring."

Said Carr, "We are carefully, and guardedly, optimistic." CAPTION: Picture, The $16 million office tower is the suburban commercial area's first major building in 10 years. By Lucian Perkins -- The Washington Post