A Montgomery County Circuit Court judge has ruled that a builder can go forward with plans to demolish a house in the town of Chevy Chase and replace it with one more than twice as large, despite a six-month moratorium on new construction passed last month by the Town Council.

Although the opinion, issued Wednesday night, applies specifically to a request by the builder, Douglas Monsein, for relief from the moratorium, Judge Michael D. Mason decided that the town had exceeded its authority in imposing the rule.

The town has 30 days to appeal.

"As I understand it, [the decision] prohibits the application of the moratorium to the builder" only, said Mayor William H. Hudnut. "It does not, as I read it, invalidate the whole moratorium ordinance."

Nonetheless, builders in town consider the ruling a de facto victory, a precedent they can use to file their own lawsuits against the moratorium or use as leverage to get the town to rescind it or move its expiration date up.

"We're totally looking at it as a victory," said Lewie Bloom, who is the informal spokesman for other builders in town. "If we have to go to court to challenge our own [projects] on an individual basis, we know we would probably win."

The Chevy Chase Town Council unanimously passed the moratorium last month after a group of residents demanded that something be done to curb "mansionization," in which older houses are being demolished and replaced with ones three and four times as large, as much as 7,000 square feet in some cases.

In Monsein's case, a 1,600-square-foot house will be razed to make way for one that will be 3,600 square feet.

Since 1997, 55 houses have been demolished in the town, a prosperous enclave of 1,032 homes off Connecticut Avenue.

As builders argued their property rights were being trampled, residents said the new houses, often derided as "McMansions," were exploiting loopholes and ambiguities in zoning rules, causing drainage problems and diminishing the "special character" of the town. A pause was needed, officials said, to consider new setback requirements and explore how to obtain more power to control development.

Many builders put plans on hold when the moratorium passed, but only two were completing deals -- Monsein, who sued, and Patrick Keating, who proposed changes in his plans that persuaded the town to grant him a waiver for two new houses.

In his ruling, the judge decided that the freeze would cause Monsein more harm than it would the town if he were allowed to build. Monsein stood to lose more than $160,000 in mortgage interest and other costs.

The judge found that the town failed to submit the freeze proposal to the county 30 days before a public hearing, as required by law.

Perhaps most significantly, the judge decided that the town exceeded its authority in enacting the moratorium. Although a municipality can impose a moratorium under certain conditions -- for public safety or to exercise existing authority to regulate setbacks, for example -- it cannot do so to seek power it does not have.

In the ruling, Mason cited "a long line of cases that the government may not use its police power to regulate aesthetics."