Kmart Corp. said Tuesday that its Builders Square subsidiary will close 15 unprofitable stores and substantially slow its conversion of existing stores to larger formats.

The closings will idle 1,318 employees, about 6 percent of Builders Square's work force. No stores will close in St. Louis; the nearest store to close is in the Chicago suburb of Schaumburg, Ill.

Builders Square, a do-it-yourself home improvement retailer based in San Antonio, Texas, said the moves will produce annual savings of about $7 million.

Rather than convert 40 existing stores to Builders Square II stores in calendar 1995 as planned, the company said it will convert 17 stores. In 1994, the chain opened 52 Builders Square II stores. By the end of this year, there will be 115 Builders Square II stores, the company said. Bloomberg

***** M. Saatchi To Leave Ad Agency He Co-founded

Maurice Saatchi will leave Saatchi & Saatchi PLC, weeks after his ouster as chairman of the sprawling advertising concern he helped found. Maurice Saatchi had been forced out as chairman under pressure from British and American shareholders, led by U.S. fund manager David Herro.

Herro and others objected to a proposed share option plan that could have been worth about $8 million for Maurice Saatchi.

Instead, Saatchi was offered the largely honorary position of president and chairman of the subsidiary Saatchi & Saatchi Advertising Worldwide, but the parent company said Tuesday that he had declined the post. …