Walt Disney Co. has agreed to buy a 33 percent stake in the digital arm of Major League Baseball in a deal valued at $3.5 billion, according to media reports on Thursday. Bloomberg News reported that the Burbank entertainment and media giant has the option to buy another third of the video streaming service of MLB Advanced Media within four years. MLB Advanced Media, in New York, is jointly owned by the 30 major league baseball teams, and provides streaming video of baseball and other sports content, including for World Wrestling Entertainment Inc.’s pay online service and PGA Tour Inc. The deal could prove lucrative for ESPN, Disney’s sports cable network, which has seen a drop in viewership in the past year, as it has an additional method for getting its programming to viewers. “ESPN has toyed with the idea of selling Web-only packages outside of the traditional cable-TV package, and Disney Chief Executive Officer Robert Iger is making deals to offer ESPN on Internet services such as Sling TV,” Bloomberg reported. Disney shares closed up 84 cents, or less than a percent, to $97.82 on the New York Stock Exchange.