Yahoo Inc., Santa Clara, CA, agreed yesterday to buy Broadcast.com Inc. in a move the Internet portal hopes will improve its distribution and multimedia abilities and give it more services for advertisers. Based on Yahoo's trading range late last week, the all-stock deal values Broadcast.com at about $5.8 billion. Broadcast.com, Dallas, sends streaming audio and video over the Internet and sells multimedia promotions to advertisers. Yahoo hopes its acquisition of the company's digital distribution network will improve its own marketing programs. With 31 million unique visitors monthly, Yahoo controls one of the Internet's farthest reaching set of properties, second only to America Online Inc.'s AOL Network. Broadcast.com delivers Net programs for BBC World Service, A.H. Belo Corp., CNN Audioselect, Major League Baseball and the National Hockey League, among others. Yahoo expects the acquisition to close in the third quarter of this year. The company said it anticipates recording a one-time charge related to the purchase but did not disclose how large it expects the charge to be. Broadcast.com stockholders will receive about three-quarters of a Yahoo share for each Broadcast.com share they currently hold. The companies did not disclose how, if at all, the merger will affect their respective employee bases.