IT ALSO ASSESSES THE EXTENT TO WHICH THESE OPERATING PRINCIPLES ARE CONSISTENTLY AND EFFICIENTLY APPLIED AND CONSIDERS THE POLICY IMPLICATION OF THESE FINDINGS FOR CONTROL OF PROSECUTORIAL DISCRETION. STUDY DATA CONSISTED OF A RANDOM SAMPLE OF NEW CRIMINAL COMPLAINTS RECEIVED BY THE U.S. ATTORNEY FOR THE NORTHERN DISTRICT OF ILLINOIS FROM OCTOBER 1, 1973 THROUGH MARCH 31, 1974. THIS COHORT WAS FOLLOWED TO DISPOSITION AND ALL AVAILABLE INFORMATION ON ALL DEFENDANTS IN EACH MATTER WAS CODED FROM FILES IN THE U.S. ATTORNEY'S OFFICE, COURT RECORDS, AND U.S. MARSHAL'S OFFICE RECORDS. STUDY FINDINGS SHOWED THAT LESS THAN ONE-FIFTH OF THE REFERRALS RECEIVED BY THE U.S. ATTORNEY FOR THE NORTHERN DISTRICT RESULT IN THE FILING OF FORMAL CHARGES IN U.S. DISTRICT COURT, AND THAT THE PROSECUTION RATIO FOR CASES WITH A SUFFICIENT BASIS TO OBTAIN A CONVICTION IS ONLY SLIGHTLY HIGHER THAN ONE OUT OF FOUR. ANALYSIS OF DECLINATION REASONS AND THE CHARACTERISTICS OF DECLINED AND PROSECUTED CASES REVEALED FAIRLY CLEAR-CUT POSITIVE AND NEGATIVE CRITERIA SHAPING THE DECISION TO PROSECUTE FEDERAL OFFENSES. SLIGHTLY LESS THAN HALF OF THE DECLINATIONS STUDIED WERE BASED ON EVIDENTIARY OR LEGAL OBSTACLES TO PROSECUTION. ABOUT ONE-THIRD INVOLVED THE USE OF AN ALTERNATIVE TO FEDERAL PROSECUTION (MOST OFTEN STATE OR LOCAL PROSECUTION), AND THE REMAINDER WERE BASED ENTIRELY ON POLICY CONSIDERATIONS, ESPECIALLY THE PERCEIVED TRIVIALITY OF THE OFFENSE. CASES INVOLVING MULTIPLE DEFENDANTS OR CONSPIRACY CHARGES WERE PARTICULARLY LIKELY TO BE PROSECUTED, AND CERTAIN OTHER KINDS OF CASES - VIOLENT OFFENSES, MAIL THEFT, AND SALES OF HARD DRUGS - ALSO RECEIVED PROSECUTION PRIORITY. EXCEPT FOR CERTAIN DECLINATIONS INVOLVING A MAGISTRATE PROCEEDING, CASES AND DEFENDANTS WERE WEEDED OUT AT THE EARLIEST POSSIBLE STAGE -- AS SOON AS IT WAS REASONABLY APPARENT THAT THE REQUIREMENTS FOR PROSECUTION WERE LACKING. (AUTHOR ABSTRACT MODIFIED)