Montgomery County Executive Charles W. Gilcchrist called yesterday for enactment of a 120-day moratorium on condominium conversions in the county, expressing concern that conversions are cutting into the stock of rental housing.

It was a reversal of Gilchrist's previous stand, and it appears to have the support of a majority of the County Council, which rejected a moratorium proposal in May.

A moratorium would go into effect upon its enactment, and Gilchrist asked the council to consider the matter next Tuesday. A moratorium would affect all buildings that had not given tenants notice of conversion and filed property, engineering and financial reports by yesterday.

"It's a 180-degree change," said Gilchrist's spokesman, Charles Maier. "What prompted this is a sudden surge in proposed conversions."

The previous week, Gilchrist had called for a continuation of the voluntary program under which developers were supposed to work with tenants and the county to ease the conversion process. At that time, the county estimated 2,559 units had been converted this year.

Since then, the county learned of developers' intentions to convert seven more buildings containing more than 4,100 apartments.

Gilchrist said this caused him "great concern about the impact of future condominium conversions on our rental stock." He further noticed in a letter to Council President Neal Potter that during the first nine months of this year, the current rental stock may be reduced by 7 to 10 percent through conversions.

"A climate of confusion and disruption . . . now pervades," he said, adding that time is needed "to establish a comprehensive and unified approach to this issue."

Gilchrist's announcement was greeted with surprise by persons associated with the real estate business and council members. Some said they think a 120-day period to work on the broader problems of condominium conversion would be useful.

"The industry and everyone involved needs to cool off and take a good, hard look at what the problems are and quit the Band-Aid approach," said Joan Hatfield, legislative liaison with the county Board of Realtors.

Richard LaVay, a developer of the Rock Creek Gardens project called the moratorium "unfortunate, it hurts property values." He said the county "should address the other side of the situation - to encourage people to build new housing."

The Apartment and Office Building Association is "strongly opposed to this legislation. It's unnecessary infringement of property rights," said Caroline Lewis, the association director of legislative affairs. "But we recognize it's an emotional issue."

"I am just absolutely delighted," said Council Member Elizabeth Scull, whose earlier moratorium proposal failed when it received only two votes. "It will give the county government a chance to decide the most effective legislation without conversions going on right and left," she said. CAPTION: Picture, CHARLES W. GILCHRIST . . . reverses stand