*** 1/2 “LOVE, JANIS” By Laura Joplin ;<i> Villard Books ($22.50)</i>

It’s not just Janis Joplin’s previously unpublished letters home that make Laura Joplin’s affectionate but never maudlin biography of her “older and more daring sister” far better than most rock personality books, though they give rare insight into one of rock’s most fascinating and tragic lives. In them, the late singer’s bottomless need for love and approval emerges with wit (she frets about becoming “the poor man’s Cher”) and sweetness (in the middle of Haight-Ashbury she asks her folks for a Betty Crocker cookbook for Christmas). But Laura, who holds a doctorate in higher education, surrounds the letters with a remarkable degree of cultural and familial context, revealing complexities of the public and private Janis.

Items in this periodic survey of pop-related books, videocassettes and laser discs are rated on a scale of one star (poor) to four (excellent).