After doubling its population three times in two generations, Montgomery County has reached the flat part of the S curve - a stage that its planners call "maturity."

Maturity is a good thing, the planners say. The breakneck pace of development has slowed down, giving local government a chance to catch up on the provision of pbulic services, such as schools, libraries, parks and police and fire protection. Maturity also means the county is no longer a bedroom of the city: 58 percent of the people who live in Montgomery work there too.

But does a mature Montgomery need a shot of Geritol? The county is becoming a place for "the top-enders and the bottom-enders," says one official, dismayed, like many of his colleagues, at the dearth of housing available for newly forming households.

The housing isn't available in large measure because the county has become so mature.

Land-use management has prevented further extension of the sprawl that still marks growth in demographically similar Fairfax County, but it has also driven up the price of land that is available for development.

There are scattered vacant parcels in the settled down-county area where modest houses could be built on small lots, but that would require zoning changes that the middle-aged residents oppose.

Then, too, maturity seems to have brought with it local government of "paralysis by analysis" described so devastatingly by staff writer Robin Reisig [Metro, July 30].

The county - that is, its citizenry as well as its elected leaders - has been unable to agree on where to build three major public facilities - a sewage-treatment plant, landfill- and sludge-composting plant. Residents in the Rte. 29 corridor and elsewhere don't want a composting plant near them. As a result, county officials have had to resort to what they acknowledge is an environmentally degrading practice - pouring sewage sludge into trenches where it putrefies for years to come. More than 900 acres of farmland and parkland have been lost for at least five years because of the trenching operations.

All these delays, one way or another, make housing development, especially in the moderate price range, less likely. Even the top-enders pay heavily. Kettler Bros. built identical houses in a Montgomery subdivision called North Farm and in a Fairfax subdivision called Wood Edge. The North Farm houses sold last fall cost $10,000 to $15,000 more than their Fairfax counterparts sold at the same time.

Part of the differential may be attributed to intangibles - Montgomery, after all, does have a 24-carat image. But one big factor was the shortage of sewered land in Montgomery.

With the mdoerate housing market drying up, county officials are detecting what appears to be a new wave of condomania. Up to now, most of the apartment conversion to condominiums has involved luxury units. But three major complexes with low- and moderate-priced units - Bradley Boulevard Apartments, Rock Creek Gardens and Piney Branch Apartments - are slated to convert.

County Executive Charles W. Gilchrist thinks the county is starting to do things on housing, and points out that Montgomery will build 25 percent of all federally subsidized housing in the area that has committed frunds. But that 25 percent only amounts to 1.864 units. According to county figures, about 22 percent of the nearly 200,000 households would qualify for low- and moderate-income assistance.

"Overall, I'm not impressed," says Gene Sieminski, the county's housing director. "We still have a helluva job to do."

Sieminski won't be around to help. Frustrated by what he sees as timid policy-makers and citzen obstructionists, he says he is quitting.