SUPPOSE YOU are a black man charged with murdering a white man. Before your trial begins, a group of prospective jurors is ushered into the courtroom and, one by one, they are questioned by the prosecutor and by your lawyer. At the completion of this examination, the prosecutor announces that he will use his peremptory challenges --he is entitled to reject up to 20 jurors without stating his reasons--and excuse jurors B, C, J and M, all of whom are black. This procedure leaves you with an all-white jury. Is this fair?

In 1964, in the landmark case of Swain v. Alabama, the Supreme Court decided such a case. There is no violation of the equal protection clause, wrote Justice White for the majority, if in an individual case the use of peremptory challenges results in the selection of an all-white jury. There might be such a violation if "the prosecutor in a county, in case after case, whatever the circumstances, whatever the crime and whoever the defendant or victim may be, is responsible for the removal of Negroes," but this was not the case before the court.

Since 1964, federal courts have adhered to the Swain decision; in some state courts, however, judges have ruled that such a racially motivated use of peremptory challenges violates the state constitution. In California, challenges may not be used to exclude jurors because of race, religion or ethnic origin. Massachusetts and New Mexico have also adopted variations on this rule. What we have, therefore, is a federal rule allowing broad discretion in jury selection to lawyers on both sides of a case, and a much stricter standard limiting discretion in a few states based on judicial interpretation of state law.

The Supreme Court accepts this diversity and this week declined an opportunity to revise the Swain standard and apply the stricter rule to everyone. A majority of the court declined to review three cases, one each from New York, Illinois and Louisiana, where the use of peremptory challenges by the prosecutor resulted in all-white juries and convictions were upheld by state appellate courts. Because this issue is of great and recurring interest, however, two separate opinions were written on the matter. Justices Marshall and Brennan believe Swain was wrongly decided and wanted to take these cases in order to overrule that decision. Justices Stevens, Blackmun and Powell write that they too would like to take another look at Swain, but not right now. They'd like to look at the experience in California, Massachusetts and New Mexico before considering whether to impose similar restrictions on all courts.

There are important questions at stake here. Does the California rule in practice, for example, require a prosecutor to assemble a jury that is racially and ethnically balanced? Is it necessary, in order to try a defendant of Albanian descent, to have someone with the same ethnic heritage on the jury panel? Have we gone too far in allowing lawyers to reject jurors for no reason, or should any citizen without bias or conflict of interest be given a chance to serve?

It is an unusually frank admission that some justices want "to allow the various states to serve as laboratories in which the issue receives further study" before they reconsider the Swain rule. But when they do reach the question, their review will have the benefit of what has been learned in California, Massachusetts and New Mexico, which should serve to make their decision practical and workable as well as constitutionally sound.