Since the summer of 1976 - when "Afternoon Delight" was a bestselling, Grammy award-winning song - the Starland Vocal Band has been a Washington group in search of a second hit record. Now Taffy and Bill Danoff, Margot Chapman and Jon Carroll are hoping a fourth album under the aegis of a new producer and new manager will do the trick. Next month the group leaves for Muscle Shoals, Ala., to record songs written primarily by Bill Danoff and Carroll. (The Danoffs have written, among others, hits such as "Country Roads" and "Boulder to Birmingham," recorded by John Denver and Emmylou Harris, respectively.) The music for their new album, says Bill Danoff, will be "multi-vocal, like 'Afternoon Delight,' with more of that and a strong rock-and-roll beat." Muscle Shoals is the small town in whose recording studios Bob Dylan just completed, amid secrecy, a new album which will express his new religious convictions in the wake of a report by a California minister who says Jewish-born Dylan has accepted Jesus Christ. Says Taffy Danoff: "I'm going to accept Robert Redford into my life. Or Jon Voight. I'll accept either as my personal savior." CAPTION: Picture, no caption