The Montgomery County Council, under pressure to expand the Planning Board's representation to high-growth areas, selected a Silver Spring woman yesterday to be the fifth member of the board.

The selection came two months after County Executive Charles W. Gilchrist vetoed the selection of a Bethesda woman for the Planning Board because the other four members were also from Bethesda, and he urged the council to consider choosing a resident of the county's booming upcounty area. The council was unable to muster the five votes necessary to override the veto, and reopened the process while promising to look hard for upcounty candidates.

After weeks of intensive debate and twice postponing the decision, the council yesterday chose Nancy M. Floreen, a 34-year-old lawyer and community activist who lives with her husband and three children in a subdivision south of Randolph Road near Silver Spring. Her appointment to the Planning Board was approved in a 5-to-2 vote, and later the council members made it unanimous.

Another Silver Spring activist, Ruby Rubens, and an upcounty area resident, Linda Bell, also were candidates for the job on the Planning Board, which, in its recommendations to the County Council, has enormous power over development issues.

Council members said they think their selection of a non-Bethesda resident will satisfy Gilchrist and others angered by the council's July 8 nomination of Rosalie Silverberg, a widely respected civic activist from the Bethesda area. Silverberg's appointment was vetoed July 21 by Gilchrist on the grounds that it was insensitive to other parts of Montgomery County where residents have been afflicted by traffic congestion, school overcrowdings and other growth-related headaches.

In rejecting Silverberg's nomination, Gilchrist said, "The insensitivity of this appointment is disturbing evidence of myopia. If [this appointment] were allowed to take effect, our Planning Board would have its entire membership drawn from a small geographical part of this county."

Council member Scott Fosler said yesterday that the July "problem was that all the other Planning Board members were from one area -- the Bethesda area and that clearly was not appropriate." In addition, Fosler said, the concentration of Bethesda representation violated the "spirit, if not the letter," of a new state law calling for broad county representation on the Planning Board.

Gilchrist indicated yesterday he will approve Floreen's appointment while at the same time expressing reservations about the geographic representation on the board.

"He would prefer an upcounty appointment," said Gilchrist's aide Vicki A. Lathom.

Yet, according to council member Rose Crenca, who nominated Floreen, upcounty leaders in this instance waged an aggressive lobbying campaign for the Silver Spring woman. "The phone calls and the letters that I have received were for Floreen," Crenca said.

The Greater Damascus Civic Association, for example, endorsed Floreen after conducting a candidate forum, Crenca noted.

A graduate of Smith College and Rutgers Law School, Floreen now is engaged in a part-time law practice, specializing in zoning matters. She also has done some work for the D.C. law firm of Rogovin Huge & Lenzner. Floreen said yesterday she intended to give up her practice to avoid any conflict with her appointment to the board.

The Planning Board position, which is considered a part-time job, pays $ 10,600 a year and provides up to $ 1,200 in annual expenses.

Floreen was appointed to succeed board member Mable Granke, 61, whose term expired June 14.