NEW YORK (Standard&Poor's CreditWire) Nov. 11, 1999--Standard&Poor's today assigned its triple-'B'-minus rating to Liberty Media Corp.'s proposed $750 million Rule 144A offering of senior exchangeable debentures due 2029. The debentures will be exchangeable into either Sprint Corp. PCS common stock or the cash value of a specific number of shares. The triple-'B'-minus corporate credit rating for Liberty Media was affirmed. The triple-'B'-minus rating on the company's $1.25 billion of public senior unsecured debt also was affirmed. Ratings reflect Liberty Media's considerable portfolio of media and related investments (both wholly and partially owned), the support that operating cash flow could offer for debt service, and the value conferred by management's long experience in the industry. These strengths