Finding moderatly priced apartments in the Bethesda and Chevy Chase sections of Montgomery County can be heavy going. The shortage of affordable rents there and in other parts of the county is painful. That makes it all the more important to prevent the loss of what moderately priced rental units there are.

Two such rental properties, the 65-unit Chevy Chase Lake Apartments and the 18-unit Fairfax Court Apartments, were scheduled recently to be sold and converted into high-priced condominiums. Rents were expected to increase by as much as 45 percent, displacing many elderly tenants. But the county government was finally able to put into effect a law passed five years ago that gives it the right to intercede and buy apartment buildings that are going to be sold and turned into condominiums.

The bill was passed during efforts to regulate a condominium conversion boom that saw one-fourth of the county's apartment units turned into condominiums in a span of only 12 years. Among other things, it gave the county the right to purchase certain units of a building to preserve them as rental units if it decided not to buy the entire complex. But so far it has proved to be too expensive to invoke the law, since the county must match the terms agreed to by the owner and another prospective buyer. In this instance, the county bought two apartment complexes for $4.3 million. It intends to preserve their moderate-range rents ($450 to $550) to hold increases for current tenants to 10 percent and perhaps to subsidize rents for some lower-income tenants.

The condominium boom has slowed considerably in recent years, but the county's purchase option still has value. Other Washington-area jurisdictions wrestling with the diminishing stock of affordable rental units should study Montgomery's condominium law