Denver-based Pace Membership Warehouse, a major player in the booming warehouse-store segment, said it plans to open a total of seven outlets next year in the Los Angeles area . . . Union Carbide said it signed a letter of intent for the sale of its Danbury, Conn., headquarters building and 650-acre site to Related Cos. of New York for about $340 million . . . Sears, Roebuck & Co. officials confirmed that they are considering ways that the company might enter the increasingly popular business of selling merchandise via television, but they declined to discuss details.