A stage actress at 10 and a member of the Swedish Royal Opera ballet at 12, precocious Marie Liljedahl--one of The Girls of Scandinavia unveiled in Playboy last June--appears, at 18, to be on her way to international sex stardom. In Inga, a Swedish-made film that has been attracting record audiences in the U. S. since November, Marie portrays a preoccupied adolescent whose aunt--in need of capital to finance her own bedroom capers--offers her to an elderly suitor. Inga loses her virginity but, in so doing, gains access to the brave new world of the senses. Like her film character, Marie is discovering herself and the new world around her. She recently left her parents' villa outside Stockholm to find an apartment in the city--but while she's attracted to the metropolis, she also finds it overwhelming and frequently sails to an offshore island, where she enjoys not only needed repose but also the chance to study future roles without distraction. Marie views her frankly erotic performance in Inga--which involves repeated exposure, a masturbation scene and some Olympian lovemaking--with characteristic Swedish matter-of-factness: "There's nothing offensive or difficult about disrobing for the camera, if that's what the script calls for. I don't get emotionally involved with the actor in a love scene nor embarrassed by the presence of the crew. We're all just doing our jobs." Marie's film career began three years ago, while she was vacationing in Greece with her family. A photographer for Germany's Neue Illustrierte approached her on the seashore with an invitation to enter a local beauty contest. Marie won easily and soon found herself studying Greek in order to act in her first film, The Hot Month of August. She then returned to Sweden, where she became a regular on television as an actress and a model. She turned down a number of roles because "the only thing the producers were interested in was getting me undressed." Inga, she felt, was a sensitive study of a young girl's coming of age. Some critics have disagreed, but the film has given Marie's career new momentum. She will soon appear in Do You Always Want to Remain a Single Girl? and--with Jacques Tati--The Sexy Dozen. After she fulfills her present commitments in Europe, Marie hopes to migrate to the States: "European men usually feel they have to try to get you into bed immediately. Americans aren't nearly as pushy--and that's a welcome relief."