Gregory B. Maffei

Liberty Media, the media conglomerate controlled by John C. Malone, agreed on Thursday to buy a stake in Barnes & Noble for $204 million, but declined to buy the bookseller outright.

The deal would disappoint investors who had hoped that Liberty, whose investments include Starz Entertainment, the home shopping channel QVC and the Atlanta Braves baseball team, would acquire a majority stake. Liberty had offered in May to buy 70 percent of Barnes & Noble for $17 a share if the retailer’s powerful chairman, Leonard S. Riggio, who controls nearly 30 percent of the company, assented.