THE TOP POSITIONS IN THE DEPARTMENT ARE COMMISSIONER, FIRST DEPUTY, AND CHIEF OF OPERATIONS. NEXT IN LINE ARE FIVE THREE-STAR COMMANDERS KNOWN AS SUPERCHIEFS, EACH OF WHOM IS IN CHARGE OF ONE OF THE FIVE BUREAUS THAT MAKE UP THE ENTIRE POLICE FORCE. THE NEXT ECHELON IS COMPOSED OF TWO-STAR ASSISTANT CHIEFS, FROM WHOSE RANKS THE SUPERCHIEFS TRADITIONALLY ARE CHOSEN. THE OCCASION FOR THE 'PURGE' REFERRED TO IN THE TITLE WAS THE ELECTION OF EDWARD KOCH AS MAYOR OF NEW YORK CITY AND HIS APPOINTMENT OF A NEW POLICE COMMISSIONER. AS IS CUSTOMARY WHEN A NEW ADMINISTRATION TAKES OVER, THERE WAS A RESHUFFLING AT THE TOP. FOUR OF THE DEPARTMENT'S SIX HIGHEST-RANKING UNIFORMED OFFICERS--THREE BUREAU CHIEFS AND THE CHIEF OF OPERATIONS--WERE ASKED TO RESIGN. THE FOLLOWING PEOPLE WERE INVOLVED IN THE RESHUFFLING: JAMES HANNON, WHO ONLY 3 YEARS BEFORE HAD BEEN SWORN IN AS CHIEF OF OPERATIONS, THE CITY'S 'TOP COP'; JOE HOFFMAN, WHO, HAVING LEFT THE DEPARTMENT AS A 'SELF-BANISHED MAVERICK,' NOW WAS RETURNING TRIUMPHANTLY AS FIRST DEPUTY, HELPING THE COMMISSIONER CARRY OUT OF THE PURGE AND RULING THE DESTINIES OF HIS FORMER SUPERIORS; AND DANIEL COURTENAY, A TWO-STAR ASSISTANT CHIEF WHO HAD BEEN PRAISED FOR HIS HANDLING OF FIELD OPERATIONS DURING THE DEMOCRATIC NATIONAL CONFERENCE BUT WHO WAS NEITHER ASKED TO RESIGN NOR PROMOTED BY THE NEW COMMISSIONER. HANNON, HOFFMAN, AND COURTENAY HAD RISEN THROUGH THE RANKS AND HAD ONCE BEEN 'COMRADES-IN-ARMS,' HAVING FACED TOGETHER A SERIES OF DEMONSTRATIONS AND DISRUPTIONS BY RANK-AND-FILE POLICE WITH GRIEVANCES AGAINST THE DEPARTMENT. THE IRONIES IN THE SITUATIONS OF THE THREE MEN ARE POINTED OUT, AND THEIR PERSONAL EXPERIENCE IN THE RESHUFFLING IS SET AGAINST THEIR INVOLVEMENT IN THE DEPARTMENT'S DAY-TO-DAY OPERATIONS, WHICH AT THE TIME INCLUDED PLANNING FOR THE VISIT OF A FOREIGN DIGNITARY. THE OFFICERS' ATTITUDES TOWARD THEIR JOBS, INCLUDING THE MIXED BLESSINGS OF BEING PROMOTED TO SUPERCHIEFDOM, ARE REFLECTED IN THEIR COMMENTS ABOUT POLICE WORK AND THE VAGARIES OF CITY POLITICS. (LKM)