Three years after Rockville completed a $24 million urban renewal project to revitalize its downtown area, city officials have asked a prominent Washington architect to devise another plan to accomplish what the original project failed to do.

Architect Arthur Cotton Moore, who designed Canal Square in Georgetown, has been selected to come up with a design to mix high-rise office buildings with high density housing units and retail stores within Rockville's business district, according to James M. Davis, director of the city's planning department.

City officials have also directed Moore to "take a very hard look" at the shopping mall called The Commons On Courthouse Square - in the heart of the city's business district - to see if it can be adapted for other uses.

The large concrete mall was the major legacy of the original urban renewal plan. In the late 1960s, 165 businesses in downtown Rockville were relocated and dozens of old structures razed to make way for its construction. It was envisioned as a "shopper's paradise," which would make downtown Rockville a hub of citizen activity both in the day and evening.

"I wouldn't use the word [failure]" to describe the mall, said Rockville Mayor William E. Hanna Jr. But, he added, "It never achieved the potential the city fathers at that time had hoped for."

Moore's assignment according to both Hanna and Davis, is not an effort to upgrade the Commons (formerly Rockville Mall), which has suffered financial troubles since it opened in 1972 because of both a high vacancy rate and stiff competition from Montgomery and White Flint malls.

The original renewal project covered only the 47-acre where the mall and its parking garage now stands. But Moore's design will encompass the entire business district, stretching north to south from the Hechinger's store on Frederick Avenue to Edmonston Drive, and from Croydon Park on the East to Rockville's West End.

But what the city officials say they expect Moore's plan to accomplish sound hauntingly familiar to the objectives of the original plan: pedestrian plazas, more walkways and open space, better traffic routes.

Davis said the plan - which Hanna says will cost about $150,000 - should also reflect the city's projected need for more high-rise and mid-level housing units to accommodate the estimated 1,700 state and county employes who will be working in downtown Rockville once the new county office building and courthouse are completed.

Davis said the downtown area can support 700 new dwelling units.

Davis said the downtown area also can support 600,000 square feet of retail space and 700,000 square feet of private office space.

Moore said he will try to bring "a sense of place, of a downtown-care" to Rockville's business district as he determines how much development should take place in the area and what should be done with the existing buildings.

Moore is the architect who restored the old Cairo Hotel and is remodeling the U.S. Post Office both in Washington. He designed the Foundry shopping complex in Georgetown and is one of the principal architects working on the development of Georgetown's waterfront. He has also devised renovation plans for downtown areas in Washington, Baltimore, Schenectady, N.Y. and Columbus Ga.

As for the existing buildings in downtown Rockville, Davis said, "We're not talking about mass acquisition, relocation or razing . . . we will work with what we've got and make it better."

He said, however, that the uses of some of the existing buildings could change.

Hanna said the outdoor shopping center behind the mall will probably not be affected by the new plan since it is doing well economically.

As Moore begins his study of the business district, Robert Gring the manager of Rockville's mall says he will continue with his plans to bring a beauty salon, a racquetball court and health spa to the mall. He said the development planned for Rockville's business district, as well as the opening of metro service there in 1981, will only enhance the economic stability of mall.

Gring has made numerous improvements at the mall since he took over as manager a year ago. He has brought flea markets, puppet and magic shows and educational displays to the mall, and has redecorated its main concourse.

"The mall will stay the mall and we will continue to progress," he said.

Moore and his associates, meanwhile, will set up a satellite studio inside the mall where they will work with city planners to decide the future of the mall and the rest of Rockville's business district.

The earlier $24 million urban renewal project was funded with about $14 million federal Housing and Urban Development (HUD) monies, with the city chipping in about $10 million.

Moore's design plan, Hanna said, should "offer such opportunities to private developers that they would be willing to come in an develop according to the plan."