IF WHITE suburbanites were victimized in disproportionate numbers by convicted criminals out on probation or parole, then there would be little policy debate about keeping violent and repeat criminals locked up.  Witness the tragic murder of” Polly Klaas, a suburban white child, at the hands of a released career criminal, which triggered a political rush toward tougher criminal sanctions. But in the 1980s, all the murders of inner-city black children at the hands of plea-bargain-gorged violent predators and drug dealers elicited no such political response.