A $48 million, 31-story office complex in downtown St. Louis, which would be the largest in Missouri, had been delayed again. The reason: the owners are concerned about rising construction prices. The office complex would provide hundreds of construction jobs and could be the key to further downtown development. The building is planned by the First National Bank in St. Louis, International Business Machines Corp. and Equitable Life Assurance Society of the United States for two-block area just west of Busch Memorial Stadium.