Admitting that "I was a stupid young boy who only had fantasies and stories in my head," author Gunther Grass attempted in New York this week to explain his joining the Waffen SS, something to which he only admitted last August. But even his sympathetic interviewer seemed far from satisfied. Grass's recently translated autobiography, Peeling the Onion, an attempt to revisit the early years of his life and to offer some explanation, brought him to the city. But he seemed unable to offer much in defense of his six decades of secrecy and his early belief in the Nazi regime. "If someone believes in something he doesn't see other things. It's easy to say I was a child, but I didn't ask any questions. That's why I wrote this book," he said.