Gen 13 would have you believe that there's a secret branch of our government called International Operations, and that IO took a bunch of ordinary teenagers, experimented on them, and turned these baffled, naive adolescents into reluctant heroes with superpowers a team called Gen 13. The most snapped-up comic on the racks the second issue already fetches $20 to $30 in comic stores Gen 13 has helped to establish its publisher, California-based Image Comics, as a market threat to DC and Marvel. The major reason is the art: As drawn by J. Scott Campbell, 22, even the fight scenes have the aura of sexy layouts. Jim Lee, 30, who writes the comics with Brandon Choi, 30, has commented that ''older people should look at [Gen 13] and be uncomfortable.'' This is a key to the book's success: The randy knowingness, combined with the kid-adventure plots and slacker-slang dialogue, renders Gen 13 a comic book as private club. It's one millions are joining.