The Montgomery County Planning Board said yesterday it "cannot support" parts of County Executive Sidney Kramer's plan allowing increased development in downtown Silver Spring because it fears the 15,000 jobs Kramer wants to add will cause "intolerable" traffic congestion.

The board instead voted to recommend to the County Council a plan permitting 13,500 additional jobs, but adding some safeguards intended to prevent overdevelopment. The board expressed reservations, however, that even this scaled-down plan could create serious traffic problems.

The shape of downtown Silver Spring's future will be decided by the council this fall in a series of decisions that essentially will determine the scale of development. While there is general agreement that the deterioriating downtown needs revitalization, an emotional conflict has formed between those favoring a massive infusion of jobs and retail stores, and area residents concerned about traffic problems and the integrity of their neighborhoods.

The Planning Board's action is only advisory, but it marks the first time a public agency has examined Kramer's plan and it reflects the serious questions that had already been raised by citizens groups.

The number of jobs that can be added without overburdening the area's traffic capacity is one of the key issues before the council. Under county law and regulations that attempt to ensure that local facilities are adequate to support development, traffic capacity now permits only 4,500 additional jobs in the Silver Spring "policy area," which also contains Takoma Park and Montgomery Hills.

Silver Spring currently has 25,000 jobs, but new projects that have already been approved will add about 7,500. Under Kramer's plan, the total employment would be about 47,500, nearly double the current level.

Kramer has proposed making downtown Silver Spring a separate central business district area and allocating it 15,000 new jobs with an additional 1,000 jobs for Takoma Park and Montgomery Hills. Kramer has proposed a variety of road and transportation system improvements as the way of meeting county policies on adequate transportation.

For example, he is proposing the establishment of a special traffic district that would use incentives to get people to ride mass transit or to join car pools. Meg Riesett, acting director of the Office of Planning Policy, said the county will increase from 20 percent to 25 percent the number of commuters traveling in car pools or by mass transit.

How realistic those transportation goals are was a major concern of Planning Board members as they wrestled with the issues this week.

In a letter to Kramer and the council explaining "the high level of discomfort" of various board members with the executive's plan, Board Chairman Norman L. Christeller said the proposed transportation system improvements hold the promise of alleviating problems, but the board wants better guarantees.

The board, while expressing support for new development, raised particular concerns about plans by the administration to divert traffic from congestion hot spots along Georgia Avenue and Colesville Road. Area civic groups have expressed their fear that heavy commuter traffic will spill onto their streets.

Riesett said such fears are premature. She said the county has longstanding policies to protect residential neighborhoods from commuter traffic and that there will be community involvement in any plan that is developed.

Silver Spring was added to yesterday's board agenda after a call from Kramer to Christeller. According to Christeller, Kramer wanted to reach a consensus with the board on a single development plan to present to the council. Kramer, according to Christeller, said he would support a planning staff's recommendation of 13,500 jobs if the board also would support it.

But the apparent compromise broke down over development safeguards -- supported by the board but regarded as unnecessary by the administration -- such as additional scrutiny of traffic flow for each new project. As a result, Kramer and the board will submit separate plans to the council.