SOCIAL AND PSYCHOLOGICAL FACTORS THAT INFLUENCE POLICE PERCEPTIONS OF AND ATTITUDES TOWARD PUBLIC PROTEST ARE CONSIDERED, TOGETHER WITH ACTIVITIES OF CROWDS (OFFENSIVE LANGUAGE, DAMAGE TO PROPERTY, PERSONAL ASSAULTS) THAT CAN AFFECT POLICE DECISIONMAKING. TACTICAL APPROACHES OPEN TO POLICE AT THE SCENE OF A DEMONSTRATION--SHOW OF FORCE, NONINTERVENTION, ARREST, DISPERSAL THROUGH THE USE OF FORCE--ARE DISCUSSED AT LENGTH, AND FACTORS INVOLVED IN DECIDING WHICH TACTIC TO USE ARE IDENTIFIED. TWO INCIDENTS OF PUBLIC PROTEST (ONE IN TORONTO, THE OTHER IN VANCOUVER) THAT LED TO THE ESTABLISHMENT OF COMMISSIONS OF INQUIRY INTO POLICE CONDUCT ARE REVIEWED. SPECIAL ATTENTION IS DIRECTED TO THE PARTICULARLY DIFFICULT POLICE TASK OF CONTROLLING DEMONSTRATIONS INVOLVING TWO GROUPS THAT ARE HOSTILE TO EACH OTHER. IT IS CONCLUDED THAT DECISIONS BY POLICE AT THE SCENE OF A DEMONSTRATION ARE BASED ON A MULTITUDE OF CONSIDERATIONS AND OFTEN MAY LEAD TO UNDUE RESTRICTIONS ON FREEDOM OF ASSEMBLY. TWO FACTORS ARE AT THE ROOT OF THIS PROBLEM: (1) A LACK OF APPRECIATION FOR THE IMPORTANCE OF FREEDOM OF ASSEMBLY IN A DEMOCRATIC SOCIETY, AND (2) FAILURE OF THE POLICE (AND THE COMMUNITY AT LARGE) TO REALIZE THAT A CERTAIN DEGREE OF INCONVENIENCE TO SOME PEOPLE IS NOT TOO HIGH A PRICE TO PAY FOR SUCH AN IMPORTANT FREEDOM. SUGGESTIONS FOR IMPROVING POLICE OPERATIONS AT DEMONSTRATIONS INCLUDE ON-THE-SCENE ASSESSMENTS OF THE COSTS AND BENEFITS OF INTERVENTION, SPECIAL TRAINING IN CROWD CONTROL, USE OF PUBLIC ADDRESS SYSTEMS AT DEMONSTRATION SITES, AND EFFORTS TO CONVINCE PROTESTORS NOT TO ESCALATE CONFLICTS. IT IS POINTED OUT THAT POLICE HAVE A LIMITED FUNCTION IN SOCIETY, AND THAT THE COMMUNITY SHOULD NOT EXPECT POLICE TO EXCEED THEIR SOCIAL AND LEGAL RESPONSIBILITIES IN CONTROLLING DEMONSTRATIONS. (LKM)