MODEL'S BLOCK

By GINIA BELLAFANTE

Ambling down runways in clothes no one buys, throwing tantrums, dating moody rock stars -- is a supermodel's life really all that satisfying? Apparently not. NAOMI CAMPBELL seems to be searching for meaning in the form of a literary career. She took a day off from the spring shows in Paris to pitch her unfinished novel at the Frankfurt Book Fair. Titled Swan, it is being called a ''sex, shopping and supermodeling saga.''