Rockville's plan to transform its failing business district into a metropolitan showplace may be in danger of falling victim to inflation.

The city planning chief, James M. Davis, said cost estimates for some of the projects developed by noted architect Arthur Cotton Moore have doubled since the plans were presented a year ago.

Next week city lawmakers will decide whether to hire an independent estimator to compile new figures based on current construction costs. Davis said the estimator's fees could run as high as $3,000.

Davis insists, however, that Moore's plan is not in jeopardy. He said when city lawmakers vote, in May, on paying for the project through the city's capital-improvements budget, they "want to make sure cost estimates are not lower than reality."

The cost of the downtown development was estimated a year ago at $2.98 million, part of which would be a one-time capital investment. Most of the plan is dependent upon investment by private developers.

Improvements to the courthouse area in the center of the city were priced at approximately $220,000 by architect Moore last year. The Public Works Department recently estimated construction and material costs for the same project at well over $1 million.

"Like everything else, construction prices have gone wacko," Davis said. "Such a variation suggests the need for an independent estimator."

Moore said the prices he placed on his plans were "guesstimates. As I see it, mine was a planning proposal." Detailed engineering plans for his proposals, which would better spell out costs to the city, are yet to be made, he said.

All of Moore's plan, which was approved unanimously by the City Council last February, could be scaled down according to the city's financial limitations, the architect said.