Warsaw's new archbishop, Stanislaw W. Wielgus, caught in Eastern Europe's widening witch hunt for former Communist secret police informers, admitted Friday that he had collaborated with the Sluzba Bezpieczenstwa, or Security Service, known as the S.B. "Before you today, I confess to the mistake committed by me years ago, just as I have confessed to the Holy Father," Bishop Wielgus said in an open letter to Polish Catholics. "By the fact of this entanglement, I have damaged the church." He said he compounded that damage by denying "facts of this cooperation" in recent days. Bishop Wielgus insisted, however, that he...