THE CENTRAL THRUST OF FEDERALISM IS A SHARING OF AUTHORITY, POWER, AND RESPONSIBILITIES AMONG CENTRAL AND CONSTITUENT GOVERNMENTS OF A SINGLE POLITICAL ENTITY. THE COMPLEXITY OF SUCH A SYSTEM IS PERHAPS MOST VISIBLE IN THE STRUCTURE OF LAW ENFORCEMENT. IN THE UNITED STATES, MORE THAN 40,000 SEPARATE POLICE FORCES ARE COORDINATED, AT BEST, BY AD HOC ARRANGEMENTS; AT WORST, THEY ARE DIVIDED BY INSTITUTIONAL AND PERSONAL RIVALRIES. IN THE U.S./MEXICO BORDERLANDS THIS COMPLEXITY AND COMPETITION IS AUGMENTED BY FEDERAL ENFORCEMENT ACTIVITY THAT IS MUCH MORE EXTENSIVE THAN IN INTERIOR JURISDICTIONS. LONG-STANDING AND CURRENTLY INTENSIFYING APPREHENSION ABOUT THE QUALITY OF 'BORDER MAINTENANCE' MAKES THE RESOLUTION OF DEFICIENCIES IN POLICE COORDINATION A TOP PRIORITY. IN EL PASO, THE PRIMARY WORK OF LAW ENFORCEMENT FALL TO THE MUNICIPAL POLICE DEPARTMENT, WHICH IS THE LARGEST FORCE AT WELL OVER 600 PERSONS. IN ADDITION, EXCLUDING PRIVATE FORCES, NEARLY 2,000 PEACE OFFICERS WORK IN THE CITY IN ABOUT 36 AGENCIES. COORDINATION IS PRIMARILY AD HOC AND DEPENDENT UPON INFORMAL PERSONAL RELATIONSHIPS BETWEEN DIFFERENT AGENCY PERSONNEL. ALTHOUGH CONFLICTS BETWEEN LOCAL AND FEDERAL LAW ENFORCEMENT PERSONNEL ARE FREQUENT AS INTERRELATED ENFORCEMENT RESPONSIBILITIES ARE PURSUED, ANY MERGER OF SEPARATE AGENCIES AT THE FEDERAL OR LOCAL LEVELS SEEMS UNLIKELY. A PROPOSAL FOR A 'BORDER MANAGEMENT AGENCY' STUDIED AT THE FEDERAL LEVEL WAS GREETED WITH INSURMOUNTABLE OPPOSITION FROM A VARIETY OF SOURCES. THE CITY HAS PROPOSED ITS RECEIPT OF FEDERAL 'IMPACT AID' TO HELP IN BEARING THE COST OF LOCAL LAW ENFORCEMENT THAT RESULTS FROM ILLEGAL ALIENS CROSSING THE BORDER--A CIRCUMSTANCE ATTRIBUTED TO THE FAILURE OF FEDERAL LAW ENFORCEMENT. THUS FAR, SUCH AID HAS NOT BEEN APPROVED. WHILE NOT SOLUTIONS TO THE PROBLEMS POSED ARE NEAR IMPLEMENTATION, THE APPROACHES TAKEN TO THE DILEMMAS OF FEDERALISM IN THIS BORDER CONTEXT MAY CONSTITUTE A PILOT PROJECT FOR OTHER LAW ENFORCEMENT LINKAGES THROUGHOUT THE COUNTRY. (RCB)