Montgomery County's Planning Board, convinced that Macy's is committed to opening its first store in the county in Silver Spring, gave another chance yesterday to the developer trying to put together a regional shopping mall some see as the spark to revitalize the downtown.

The Planning Board voted 4 to 1 to give developer Lloyd W. Moore until January to get another department store and other tenants for a $250 million retail, office and hotel complex that would establish Silver Spring as a major regional shopping destination.

The board's decision, the latest chapter in Montgomery's long-running debate over Silver Spring's future, was a sweet victory for Moore. He has spent more than three years and millions on a project that has suffered a series of setbacks and antagonized much of the Silver Spring community even while being strongly backed by county officials.

"It's been very difficult," said Moore, "but never, never did I ever doubt that Silver Spring could attract a first-class retail development . . . . This is a victory for the Silver Spring community."

The Planning Board's decision comes just eight days before a critical deadline that could have voided approval of the project planned for Georgia Avenue and Colesville Road.

The board, which has the final word on whether projects can be built, had originally given Moore a June 29 deadline to provide evidence that he could attract two big-name department stores to Silver Spring.

Once a thriving commercial center, Silver Spring saw the exodus of stores to suburban shopping malls that left its downtown dowdy and vacant. There has been a boom of office building in recent years but little of the stores, restaurants and other entertainment that make for a thriving downtown.

Even though Moore admitted he hadn't fully met the conditions -- he still must land another department store to anchor the project -- he asked the board for more time.

"Silver Spring is on the verge of its rebirth," said Stephen J. Orens, Moore's attorney, as he urged the board, "Don't throw away what we've done . . . don't say no to Macy's."

The board's Silver Spring meeting room was packed with residents on both sides of the issue. Those opposed to the project because of the traffic it will produce, its design and because historic buildings will be destroyed argued that Macy's nonbinding expression of interest is a flimsy promise full of conditions and caveats and not the commitment demanded by the board.

The letter is "hocus pocus," said civic activist John Gilson.

However, board members said they were convinced that R.H. Macy and Co., which signed an agreement with Moore on Monday, is intent on coming to Silver Spring by the planned opening date of fall 1993. Planning Board Chairman Gus Bauman said the board was particularly impressed by a telephone conference it held with Harvey Samuelson, Macy's vice president of real estate.

"We peppered him with questions. It was an hour of cross-examination and I have no doubt that if Lloyd can put this project together, Macy's will be here opening its doors," Bauman said.

Board members were also persauded by testimony that even though the agreement is nonbinding, Macy's has never in its history backed out of such a deal.

Bauman was the only board member to vote against the extension for Moore -- even though he voted for the project when it was approved in January. The Planning Board has twice approved Moore's proposal because the county's 1988 approval was ruled invalid in the court case now before the Maryland Court of Appeals.

Bauman said he voted against the project "because I see no end to this." He said that the redevelopment of Silver Spring has been put on hold for too long because of the uncertainity over the Moore project. Board member Nancy Floreen, who has consistently opposed the project, favored the extension, saying it would be short-sighted "to pull the plug at this time" on a project that twice was endorsed by a majority of the board.