The Montgomery County Council imposed a nine-month moratorium last night on converting apartments to cooperatives and the sale of memberships in such conversions.

The move came almost a year after the council imposed a similar moratorium on condominium conversions and is designed to give county officials time to close what they perceive to be a loophole in laws governing conversions.

County Executive Charles Gilchrist called for the new moratorium two weeks ago when rumors circulated that the 1,000-unit Promenade Apartments in Bethesda would be converted to a cooperative.

The law governing conversions applies only to condominiums. It allows tenant organizations or county agencies 120 days to buy the buildings proposed for condominium conversion and levies a 1 percent transfer tax on all rental units sold.

Initially, it appeared that American Invsco, the new Promenade owners, had circumvented county condominum laws by converting the building to a cooperative. The moratorium, however, is retroactive to July 9 -- the day before American Invsco announced its intention to convert -- and legislation imposing restrictions similar to the condominium law is expected to be introduced in 60 days.

In addition to the moratorium, the council voted to implement two other measures designed to ease problems caused when tenants are forced to move during a conversion.