IF ANYTHING is going to halt the deluge of costume sword fighting epics that have flooded the local market since last year, it is the sameness of the plots and action scenes. With its glossy sheen and first rate cast, Butterfly and Sword probably ranks as one of the better examples of the genre. Some shots are beautiful, the moonlight streaming through the trees as blue banners unfold and sway in the wind. The scenario, alas, unfolds in more pedestrian manner. Butterfly and Sword may be pretty to the eye, but proves to be an unsubtle ''adventure'' of good versus evil told against the backdrop of a humdrum love rectangle that fails to add spice to the proceedings. The story focuses on a band of merry men, orphans raised by Big Sister Ko (Michelle Yeoh), who live in the Happy Forest. Ko is a female Robin Hood whose kung fu is more than the equal of her male rivals'. She is at a disadvantage, though, when faced by her female rival, B utterfly (Joey Wong). Theirs is a battle over the affections of Star (Tony Leung), who loves Butterfly and treats Ko like a sister. Meanwhile, ''little brother'' Yip (Donny Yen) pines for Ko, but it is a case of unrequited love. When not lusting over one another they fight the bad guys, but you never care enough about the characters to be unduly concerned about who lives and who perishes. Eighteen-year-old singing idol Jimmy Lin has the most thankless part of all. Lots of action in his few scenes does not make up for the fact that although he may play a prince, his role is so insignificant it appears to have been tacked on after the script was completed to give this Hongkong-Taiwanese co-production more box-office power in Taiwan.