Primestar Partners Inc. agreed to buy the large-dish satellite TV business of United Video Satellite Group for $480 million. Primestar hopes to switch its 1.2 million subscribers to Primestar's direct-broadcast TV service to better compete with industry leader DirecTV. Primestar will issue about $430 million in convertible preferred stock and assume $50 million in liabilities to buy Superstar/Netlink Group from United Video, Liberty Media Group Inc. and Turner Vision Inc. The United Video unit is the biggest U.S. provider of C-band, or large-dish, satellite programming. Englewood, Colo.-based Primestar, which is owned by several cable-TV companies, said it will offer United Video's subscribers a chance to switch at "very attractive" rates.