JUST THE OTHER DAY, we noted that the existence of the death penalty changes and sometimes distorts the criminal law. If we had waited a few days, the Supreme Court would have made the point for us. Last week, it carved out an exception to its traditional reading of the Constitution so that John Bullington, who escaped a death sentence the first time he was convicted of capital murder, won't have to face the death sentence when his case is tried the second time.

The decision drew a sharp dissent from four justices. Speaking for them, Justice Powell observed that the court had never previously said the double-jeopardy clauses applies to sentences; it had only used that clause to rule that a person who has been acquitted of a crime cannot be tried again for the same crime.

History and logic are on Justice Powell's side. There are a half-dozen or so old decisions that say explicitly that a more severe sentence can be imposed after a second trial following a reversal of the original conviction. Since a death sentence is, first and foremost, a sentence, those precedents would logically require the court to let Mr. Bullington and others like him risk death a second time.

But, as Justice Holmes wrote years ago, "The life of the law has not been logic; it has been experience." A majority of the court found something in that experience, which led it to stretch the old rules. That something, never quite articulated, is that it is worng for the government to ask a second jury to impose a death sentence in a case in which the first jury refused to do so.

To avoid permitting that, the court ruled that the procedures installed by the state of Missouri (and other states) for deciding who is executed and who is not amount to trials, for all practical purposes. Under those procedures, a person convicted of capital murder faces a second hearing before the same jury. Additional evidence is presented, and the jury decides whether the appropriate penalty is death or life imprisonment. By calling that second hearing a trial, the court had no trouble fitting the old rules to it, since they bar prosecutors from getting a second chance at convincing a new jury to do what the original jury refused to do.

This is probably the least disruptive way the court could have reached such a result. The new rule affects only death penalty cases. It is not especially logical; it breaks sharply with precedent, and it may turn out in the long run to have peculiar and unanticipated effects on sentencing procedures in general. But that is the kind of thing that happens again and again when the judges face up to the question of life or death.