R.H. Macy & Co., one of the nation's leading retailers, signed an agreement yesterday indicating interest in opening its first department store in Montgomery County in a downtown Silver Spring mall, just 11 days before the developer faces a critical deadline to sign up two anchors for his controversial project.

"This should show the county planners that Macy's has a very high interest in having a store at this location," said Harvey Samuelson, Macy's vice president of real estate. He said the New York firm has entered into a "nonbinding" arrangement with Lloyd Moore, who is trying to develop a $250 million retail, office and hotel complex in the heart of downtown Silver Spring.

It was unclear, however, whether the letter from Macy's will satisfy Montgomery County planners who -- frustrated by more than three years of delays and setbacks in Moore's project -- set a June 29 deadline to show he can fulfill his promise of bringing two big-name stores to the aging downtown.

"How solid is Macy's commitment? And what about the second store . . . . Those are the critical questions," said county Planning Board Chairman Gus Bauman.

The board, which essentially has life or death power over building projects, is set to meet Thursday on the Moore project.

Moore said he believes his letter from Macy's is powerful evidence that he has a viable project, and he will ask for a six-month extension to come up with the second department store and to continue work on his project.

If that request is denied, board members have said they will look at alternatives to a regional mall for the redevelopment of downtown.

Macy's, which entered the Washington market with a store in Tysons II in 1988, has been looking to open a store in Montgomery County, but its attempts to locate in White Flint Mall were rebuffed under county rules limiting growth. Recently, analysts say, the company has suffered a cash flow problem that makes expansion difficult. In addition to the stores it operates in northern Virginia, Macy's has stores in the Baltimore area.

The Planning Board, in the face of unprecedented opposition from residents, twice has given Moore its approval to go ahead with his project planned for eight acres at Colesville Road and Georgia Avenue.

The board's 1988 endorsement of the so-called Silver Triangle project was overturned by a circuit court judge who ruled that the county used invalid procedures.

Moore appealed the decision, in a case to be heard the Maryland Court of Appeals, but he also returned to the Planning Board for a separate new approval. He received a new endorsement in January -- but it came with a host of conditions from a board impatient with the project's pace.

Moore, who issued a news release yesterday moments after the agreement was signed, said he was "euphoric" and that the letter means that "R.H. Macy has a written agreement with us."

"They intend to open up a store with us in Silver Spring" and "the basic business terms of our deal have been worked out," Moore said. He characterized the agreement as a letter of intent -- "the basic documentation which is used by department stores to show that they wish to open a store in a particular project."

"We signed an expression of interest," said Samuelson, who took pains to say it was not a "letter of intent." He stressed that the document was nonbinding.

"It means we have a very high level of interest in joining the project if the developer can put it together," Samuelson said.

Sources knowledgeable about retailing said a letter of intent is evidence that a company is serious and generally precedes the signing of a lease.

Bauman said attorneys for the Planning Board will examine the documents.

County Executive Sidney Kramer, who strongly backed Moore's project at some political risk, said he is pleased that a retailer of such prominence as Macy's has expressed an interest. "This shows a genuine interest," Kramer said.