KISS AND TELL

Last week some of network news' hottest couples were overcome by spring fever. *At the press conference announcing the appointment of Connie Chung as co- anchor of the CBS Evening News, an ebullient Dan Rather hugged his new partner three times and kissed her twice. *During ABC's fall TV preview at Carnegie Hall, 20/20 anchors Barbara Walters and Hugh Downs coyly ad-libbed sexual innuendos in front of 1,200 advertisers and reporters. *In a promotional video, NBC's Mr. Button-Down, Tom Brokaw, unexpectedly dipped Today show cohost Katie Couric. What's behind this local-news- style romantic chemistry? According to media critic Jon Katz, ''People want to see a happy couple reading the news. The only thing the networks are missing is the jolly weatherman.''