Crime and evidence

The United States Supreme Court has ruled that incriminating evidence, if obtained ''in good faith'' by police even though unanticipated in a search warrant, need not be excluded from a trial.

In one sense, this will be a popular ruling. The issue of evidence, or more precisely the ''exclusionary rule,'' runs along a political faultline, dividing those who would like to see more effective police action against crime and those who are apprehensive that Fourth Amendment protection against unwarranted search and seizure will be abused. It would seem that the court majority has sided with the view of many Americans who think that criminals too often go free on ''technicalities.''

The Supreme Court does not deliberate in a vacuum remote from public opinion. Justice Byron R. White, in the majority opinion, observes the need to avoid ''disrespect for the law and the administration of justice.'' Other important decisions, such as the 1973 ruling upholding a woman's right to seek an abortion , have been preceded by shifts in the general public's views.

In this instance, the number of criminal cases affected by the ruling is small, in the 1 to 2 percent range. A more crucial test of the law could come next year, in a Supreme Court decision on exclusion of evidence taken by police, without a warrant, who mistakenly thought they were acting properly in a search.

Neither side can confidently predict the practical effect, on the legal system or on crime, of this second shaving back of the interpretation of seizure-tainted evidence. (A month ago the court approved a general practice of admitting illegally obtained evidence that would have inevitably been discovered anyway.) Justice Harry A. Blackmun, who voted with the majority, acknowledged the experimental side of the ruling. He said the opinion's assumptions were ''provisional'' and ''now will be tested in the real world of state and federal law enforcement.'' ''If it should emerge from experience that, contrary to our expectations, the good faith exception to the exclusionary rule results in a material change in police compliance with the Fourth Amendment, we shall have to reconsider what we have undertaken here.''

We are more comfortable with this more modest assessment of the court's conclusion.

So many of today's attitudes on crime appear generated in a world of drug-related offenses, which many readily perceive as a social threat that defies familiar legal and societal defenses. What would be the view if the cases at hand involved political dissent, and the issue were unwarranted police search and seizure of evidence? Would not the case for basic constitutional safeguards against potentially repressive intrusions be easier to see than in the current climate of drug-related and violent crime?

Systems of justice cannot cut their cloth to suit the classes of crime of the times. Bill of Rights protections of individual liberty, which require the agents of goverment such as police and magistrates to conform to rules of evidence, were included in the Constitution to distinguish the American democracy from other polities that preceded it. Today they still distinguish the United States from repressive states.

Justice White acknowledged this concern in affirming that evidentiary standards such as ''probable cause'' will still have to be met.

If the Supreme Court's latest leanings suggest a more determined effort in society generally to curb crime, it could prove useful.

It would be unfortunate to expect too much, however, from minor adjustments to the exclusionary rule.

A legal system for justice is not a wholly precise machine. Society will have to advance in the widest range of moral concerns - in personal and business ethics, in the responsibility of raising children and caring for elders, in the distribution of opportunities and encouragement of the unfortunate - to deprive crime of the mental darkness on which it feeds.