EVERY day, Will Hertzberg owns a little less of his three-bedroom house in Corona. Like hundreds of thousands of other homeowners around the state, Hertzberg has a mortgage that lets him choose how much he pays each month. ADVERTISEMENT Like many of them, he always chooses to pay as little as possible. For the moment, this allows the 56-year-old Hertzberg to continue living in his tract home despite being only marginally employed. But his debt is swelling, and his mortgage company controls his fate. "I am rather screwed," he said.