The Montgomery County Planning Board, dealing a severe blow to the American Speech-Language-Hearing Association's plan to develop an office park at its Bethesda headquarters, is recommending that the county deny the group's controversial rezoning request.

Concurring with its planning staff, the five-member board unanimously decided last week that the proposed commercial rezoning would violate the county master plan, which recommends that the land be used for residences.

The board also determined that a rezoning of the 11-acre property, located at Rockville Pike and Strathmore Avenue, would set a precedent that ultimately could change the character of the surrounding residential area.

The board's decision is scheduled to be considered by a hearing examiner Sept. 9 before the proposal goes to the County Council for final action.

A standing-room-only crowd of about 100 residents from Garrett Park and other nearby areas cheered and applauded the board's ruling. Opponents have objected to, among other things, the extra traffic that they say would spill from the development onto Strathmore Avenue, a residential street that slices through Garrett Park.

"We're very pleased with the decision," said Garrett Park Mayor Laura C. (Peggy) Pratt. The Town Council and the Garrett Park Citizens Association voted to oppose the association's plan last fall.

The 20,000-member association wants to build four "low-rise" office buildings, which would contain up to 350,000 square feet of space, and lease the space to other groups to generate income for its programs, Executive Director Frederick Spahr said. The association represents practitioners who work with individuals whose speech, hearing or use of language is impaired.

The plan calls for a 1,100-space underground parking garage.

Spahr said he disagreed with opponents' concerns that the development would set the stage for major commercial development. The association's headquarters, like other nearby chunks of undeveloped land, is located near the new Grosvenor Metro station.

"There is no legal precedent," Spahr said. "And if there is a precedent, what we have proposed, with low-rise buildings, 50 percent of green space and underground parking, we think those are all attractive features."

Spahr said that the association has tried to ease citizen concerns about the extra traffic along Strathmore by proposing to build an access route from the office complex to nearby Tuckerman Lane.

Planners estimated in a recent report that the development would attract 1,575 workers daily. Such a traffic increase, planners warned, "would take away road capacity that is needed for future development at the Grosvenor and White Flint Metro stations."

The association, without citizen opposition, built its 40,000-square-foot headquarters in the mid-1970s under an exception to county zoning laws that permits nonprofit, philanthropic groups in residential areas.

Spahr, noting that a final decision on the proposal rests with the County Council, said that the board's ruling would not affect a recent agreement it negotiated with a Boston developer and the Strathmore Hall Foundation, a nearby county-owned arts center.

The agreement calls for the association and developers Spaulding & Slye Inc. to give the foundation $75,000 and $495,000, respectively, if the rezoning is obtained and the developer is allowed to build the proposed access road through foundation property.