Larry J.B. Robinson, who 10 years ago sold the 96-store jewelry chain that bears his name, yesterday announced that he is getting back into the business, acquiring Rockville-based Royal Diamond Jewelers for undisclosed terms.

The acquisition of Royal, a chain with 12 stores in Maryland and Virginia, represents Robinson's bid to reenter the competitive local retail market, in which he built J.B. Robinson Jewelers from one to 96 stores after inheriting it from his father.

Robinson sold the J.B. Robinson chain for undisclosed terms to W.R. Grace & Co. in 1979 and ran it for seven years.

Grace sold the chain to Kay Jewelers Inc., the Alexandria-based national jewelry retailer, in 1986 for $55 million in cash. As part of the sale to Grace, Robinson signed an agreement that prohibited him from opening new jewelry stores. That agreement expired early this year.

Privately held Royal will be one of two divisions of Robinson's growing jewelry company. The other is the Antwerp Diamond Centres, a recently founded upscale chain whose first store opened in Cleveland in June. Robinson said he plans to open two Antwerp stores in the District this year and one next year.

Robinson said he plans to leave Royal basically intact. "Currently, we don't plan any major changes in Royal Jewelers' personnel or merchandising policies," he said.

But he said his plans for the chain included opening Royal stores in the District, increasing the chain's diamond inventory and remodeling store interiors.

"Royal owner Cecil Royal {owner of Royal} and I have been friends for about 20 years," Robinson said.

"The locations are outstanding, the people are very good and I have great confidence in the future of the greater Washington market."

Robinson conceded that he may be one of few business executives optimistic about growth prospects for the area's sluggish economy. "This is a time of opportunity for someone like me who has a little cash," Robinson said. "I couldn't be happier about reentering the jewelry business."

During his absence from the jewelry trade, Robinson has not been idle. He is chairman of Robinson Venture Capital and the Robinson Consulting Group and is co-owner of four radio stations.