Montgomery County's school and planning boards are hammering out a policy that will make it easier for the county to block new housing developments if there is not enough school capacity to accommodate new students.

Board members discussed the policy last week at a meeting they called productive, but spokesmen for both boards later disagreed over how far the county must go to prove that school capacity cannot sustain new residential development.

"The plan seems to call for continuous, time-consuming calculations in each and every development," school board President Robert E. Shoenberg said in an interview. "It just doesn't seem reasonable."

But Norman L. Christeller, chairman of the planning board, said the county must be careful to provide detailed and balanced information when it rules out new developments, or the decision will not hold up in court.

"If there is an appeal to the court, we have to have something solid to stand on," he said.

Planners have been grappling with the controversial issue for almost six months, since the County Council requested that they to use school capacity as a basis for denying development under the county's Adequate Public Facilities Ordinance. That law allows new developments to be blocked when there are not enough public facilities, such as roads, sewers or schools, to accommodate new residents.

The council's request came shortly after an announcement by the school board that it needed $248 million for new school construction and additions to existing schools to meet enrollment projections.

The development policy is wildly unpopular with developers, who say the county is obligated to provide new services for its citizens. Even some planning board members balked at denying new subdivisions solely on the basis of school capacity because, they said, it is too subjective and a decision based on capacity would not hold up in court.

Over the past few months, the planning board has deferred one proposed subdivision because of inadequate school capacity. The developers of several other projects voluntarily have asked for deferrals until a policy can be worked out. But the planning board went ahead and approved a handful of subdvisions that school officials said should not have been endorsed.

The two boards now are meeting to work out a process that can be used to determine whether a subdivision will create more students than local schools can accommodate. Board members say there is a spirit of cooperation between the boards, but acknowledge there are inherent differences that must be overcome.

The school board is elected and is legislative in nature.

The planning board is appointed and its decisions are quasi-judicial.

"The planning board has a much more rigid way of operating, while the school board has much more discretion," Christeller said. "We have to be consistent with guidelines because our decisions are of a judicial nature and can be appealed to the courts."

Consequently, the planning board wants a detailed analysis of each subdivision proposal so it will have something to show a judge in the event of an appeal, he said.

Shoenberg said he understands the concerns of planning board members but feels the county has more leeway in making judgment calls about school capacity.

"No matter how many procedures you have, in the end it is a judgment call," he said. "One we can make . . . without undue burden."

Schoenberg said school capacity is not as flexible as it seems. Boundary changes are discouraged because they disrupt a community, he noted, while portable classrooms can alleviate overcrowding only slightly because libraries, gymnasiums and cafeterias in the main buildings are limited in size.

County school policy is to keep schools at 90 percent of capacity to ensure that an excellent quality of education is maintained, said Shoenberg.

"Maximum learning opportunity is by itself sufficient grounds to deny or defer development without going into elaborate calculations," he said. "We are equipped to make these judgments . . . to determine what is the straw that will break the camel's back."

Both Christeller and Shoenberg said last week's meeting helped planning board members understand the limits of school capacity.

"For educational reasons, there are real limits on flexibility," said Christeller. "Some planning board members were unsure about that and I think the school people went a long way in explaining why they are not as flexible as was thought."

In turn, planners wanted to impress on the school board members the need for consistency, which both spokesmen agree was accomplished.

The school board will discuss the development policy at a meeting this month and will then get back to the planning board.