The Montgomery County Planning Board this week approved annexation into Gaithersburg of a 148-acre parcel, asking that it be granted a denser zoning that has been hotly contested by neighboring residents who say the proposed subdivision would further jam traffic and would be incompatible with their own neighborhoods west of I-270.

In a 3-to-1 vote Thursday, the board approved a motion that would allow up to five units per acre on a tract northeast of Muddy Branch Road and Route 28, currently part of the Washingtonian Country Club golf course. That action trimmed a request by the developer, Jay Alfandre, to 710 units from 748. Citizens groups had asked it be limited to 400 units.

The board stipulated that Alfandre must make good on various concessions, including contributing money to widen Route 28, building at his own expense two lanes on Muddy Branch Road and selling up to 50 percent of his houses at "moderate" prices, around $70,000.

Homeowners in the subdivisions of Dufief, Westleigh, Shady Grove Village, and Brighton and other neighborhoods around the golf course railed against the proposal at hearings before Gaithersburg's Planning Commission and City Council in the spring, urging the city either to cut back the density they would approve, or at least wait until the county approved that part of the county master plan which is currently under revision.

Now that the county planning board has endorsed this sector of the plan, a proposal goes to the county council which in turn will instruct Gaithersburg's council whether to accept the denser zoining. The county is expected to decide before Gaithersburg's next council meeting May 2.

Civic groups maintain that the notorious traffic jam along Route 28 at rush hour would be worsened and city officials from Rockville and Gaithersburg at early hearings asked the county planner to set more money aside for improving crowded roads and to take that money from the more than $70 million scheduled to go into roads where the county wants to bring new development.

"We ought to be very disappointed," said Diane Aronson, vice president of Westleigh Citizen's Association, an organization whose neighborhood is adjacent to the golf course land. "We felt the road conditions should have limited the development. We're hoping that the city of Gaithersburg will be more sympathetic to the residents of the area."

She said the hearings before the county planning commission have been disillusioning. "We are just wondering when the voices of the citizens of an area are going to be given as much weight as the voices of developers. We have attended all the hearings and we've never changed our opinion, yet not one of our concerns was addressed adequately by the planning commission."

Alfandre said he was "very happy" with the decision, and would be eager to pursue his plans, which should reach the construction stage by next winter.

He said he felt satisfied that he met many of the citizens' concerns. "We had gone in asking for six units per acre, which would have been around 900 units," he said. "After our negotiations with the city and the citizens, we brought it down to five units per acre."

Besides the road improvements, Alfandre said he would also build a 46-acre park as part of the arrangement.

Citizens' groups are expected to ask the county council to turn down the proposed denser zoning. Under a special county law, if the council rejects an annexation proposal that requests denser zoning, that rejection locks in the current, lower zoning for five years, according to Perry Berman, chief of planning for Northern Montgomery County.

In other actions, the planning board removed 87 and added 14 sites to the county master plan for historic preservation. The board also decided that multimillion-dollar office and shopping arcades proposed for downtown Bethesda--one at 4600 East-West Highway and another at 7700 Wisconsin Ave.--would meet the zoning requirements and would be considered for later approval.