Two United States Supreme Court death penalty decisions within the last week have settled two important constitutional issues: Executing the mentally retarded is cruel and unusual punishment in that it holds culpable those otherwise deemed incapable of informed decision; allowing judges to impose the death sentence violates the right to trial by jury.

These are landmark decisions, certainly for the estimated 350 mentally retarded person now on death row and the nearly 800 there by order of a judge. Beyond those immediately affected, death penalty opponents hail them as solid blows against a punishment they see as inhumane in any application. Proponents say these are mere adjustments to the ultimate and necessary deterrent to crime.

Those conflicting interpretations should be an indication of the legal blizzard to come. Both rulings are retroactive, meaning that at least 350 cases in the 20 states that allow the execution of the mentally retarded will be reviewed, as will the nearly 800 in nine states where judges make the final call.

And that will be just the start. Since there is no generally agreed-upon definition of mental retardation, states have widely varying standards and methods of testing; already claims of mental retardation are being made by inmates who made no such claim before. Since most states that allowed these executions had no reason to test for competence before sentencing, just sorting out the capable opportunists from the genuinely afflicted will be a nightmarish task. Then, of course, those states will have to re-craft their death penalty legislation to include mental-capacity testing that will withstand challenges.

While this death penalty decision completely reverses one made just 13 years ago in which the court found nothing cruel or unusual about executing the retarded, the trial-by-jury decision continues a line of thinking the court embarked upon two years ago when it ruled that that constitutional protection extends beyond the trial itself to the fact-finding phase of sentencing. Some of the 800 are on death row solely because of a judge’s decision, some are there after a jury made an advisory recommendation of death to a judge, adding to the complication are the formidable procedural barriers to sentencing review in many states.

Those controversies aside, these decisions are wise. Further, they add to the growing body of evidence that the one criminal sanction that must be free of error can never be that. Scores condemned people have been found truly innocent in recent years thanks largely to DNA evidence. Now, it is known that the crucial determination of mental ability to understand consequences is haphazard and the high correlation between death sentences and elected judges has been exposed. In these decisions, however, the Supreme Court upheld the validity of the death penalty in general. Taking that next step will be up to Congress and state legislatures.