ROCK/POP Diana Ross: ''Silk Electric.'' (RCA. AFL1-4384.) Diana Ross's transmutation from '60s motowner to '80s pop dazzler has taken its toll. Her carefully calculated music does accomplish its task of easing itself into today's pop mainstream, but it lacks the freshness of some of her earlier work. Nonetheless, Miss Ross can still turn on the style in a way that settles any argument about her excellence as a singer. The second side of this LP appealed more to this listener. Songs like ''Anywhere You Run To'' and ''Who'' are bright and compelling. On the other hand, her journey into the land of hard rock in ''Fool for Your Love'' seemed a lot of effort for little enjoyment - either for the listener or Diana. We suggest she leave the harder stuff to the Billy Squiers of the world. This LP has produced a hit single in ''Muscles,'' but apart from the cynical (and we found, distasteful) theme of this number, the music itself was smooth and fresh-sounding enough.