Montgomery County Executive Charles W. Gilchrist, responding to appeals for more upper-county representation in decisions about land development, plans today to veto the appointment of a Bethesda resident to Montgomery's powerful Planning Board, according to a source familiar with the executive's decision.

Gilchrist's veto, which he is expected to announce at a morning news conference, follows an intense 10-day campaign by community groups and political leaders from the upper county to block the County Council's July 8 appointment of Rosalie Silverberg, a longtime resident and civic leader in the southern part of the county. An aide to Gilchrist would not comment yesterday on the impending veto, which was confirmed by a public official who asked not be identified.

The council's appointment of Silverberg, 74, to a five-member board that already includes four residents of the Bethesda-Chevy Chase area, angered upcounty activists who desire a greater voice in the planning agency. In Montgomery, where public debate over land use is almost a religion, the planning board wields tremendous influence by approving or rejecting development and zoning plans.

Critics of Silverberg's appointment said that with an all-white, Bethesda-controlled board, the council should have chosen another contender -- Ruby Rubens, 51, who is a black and who lives near the congested Rte. 29 corridor in eastern Montgomery County. That area is experiencing many of the same problems of rapid growth as the upper county.

"We just think it's ridiculous that the only people ever qualified to sit on the planning board are ones that have Bethesda addresses," said Linda Bell, chairman of the Committee for the Upcounty, a coalition of business and civic leaders. Bell said she applied for a seat on the planning board two years ago but lost to a Bethesda resident.

Supporters of Silverberg, a retired biochemist, argued that she was the most qualified candidate for the job, with several years of experience as a highly respected community leader who sat on public commissions and boards. "There's nobody in the county right now that knows more about the intimate details of the planning process and has given more time and effort," County Council member Esther P. Gelman said of Silverberg. Gelman, a former planning board member, was a strong supporter of Silverberg's appointment.

Many of Silverberg's opponents did not dispute that she was qualified." It's not a question of her qualifications, which I understand are excellent, but rather a matter of geographic representation on the board," said Ed Gannon, a Republican candidate for county executive who urged Gilchrist to veto Silverberg's appointment.

"It is easy to understand the outrage of residents of the upper county," said Gannon, who lives in Bethesda. "They live with bumper-to-bumper traffic and overcrowded schools. Yet they feel they have very little say in the decisions that would alleviate these problems."

Gilchrist's impending veto was the talk of a political fund raiser held Saturday night by the Eastern Montgomery-Kensington-Wheaton Democratic Club. Council member Michael L. Gudis, a strong supporter of Rubens, said he approached Gilchrist at the party in Spencerville to say he had heard that the executive was inclined to veto Silverberg's appointment.

Gilchrist was noncommittal, he said, but Gudis, an upcounty resident, said he used the occasion to make a final pitch for Rubens. "The bottom line is that Ruby Rubens should be on that board," Gudis said in an interview yesterday.

Gudis would likely be a key vote in any council effort to override Gilchrist's veto. Were Gudis and two other Rubens supporters to stand firm, it would be impossible for Silverberg's supporters to muster the five votes needed to overturn a Gilchrist veto.

If the seven-member council fails to override the veto, it could consider the previous finalists for the planning job or reopen the appointment process.

Gilchrist, according to associates, believes that council members ignored the spirit of a new state law requiring the council to consider "geographical balance" when making planning board appointments.

State Del. Gene W. Counihan, who represents the upcounty community of Montgomery Village, cosponsored the key legislation in the 1986 session of the General Assembly and cited the new law last week when urging Gilchrist to veto Silverberg's appointment.

"Charlie was concerned about the Silverberg appointment from the beginning," Counihan said yesterday. "His view, like ours, was that it was just outrageous."