THE SUPREME COURT kicked off its term with an unusual afternoon argument concerning how to contain the damage it has wrought on criminal sentencing in America. Nominally, the question before the court was whether to apply last term's reckless decision in Blakely v. Washington to the federal sentencing guidelines. In Blakely, an ideologically diverse, five-member majority insisted that facts that jack up a defendant's sentence beyond the presumptive legal range must be proven to a jury, not to a judge. Since federal sentencing under the guidelines depends in many cases on facts proven to a judge, the new cases have the potential to invalidate the entire system under which criminals are sentenced under federal law.

This result seems all but preordained. The principle the justices articulated last term would seem to require that the guidelines get tossed. So the real question is probably not whether the guidelines will fall but how they will fall -- and how much further disruption that will cause.

Blakely has already been an earthquake, casting a huge number of federal sentences into doubt and hovering over nearly all pending federal cases. The decision is superficially attractive in large measure because the guidelines themselves are badly flawed. The combination of their rigidity and the stiff mandatory minimum sentences Congress has required in drug cases cause real injustices. People are sometimes sentenced to long prison terms because of facts not proven to the juries that convicted them. The reality, however, is that nothing in this bizarre chain of Supreme Court cases prevents a judge from throwing the book at a defendant based on facts outside of the jury's verdict -- or even based on whim.

Any system that could realistically replace the guidelines is likely to be far worse from a civil liberties point of view. The decision's defenders pretend that Congress might replace the guidelines with a system that allows judges to dispense mercy more easily. More likely, Congress -- which has acted so consistently to force judges to sentence more harshly -- would simply replace the relatively nuanced guidelines with the crude mandatory minimums. In the short term, current defendants may benefit from the guidelines' collapse, but in the not-so-long run, the system is likely to be less fair.

The justices appear to have already whistled past this particular graveyard. It is critical, however, that they proceed more responsibly than they did last term. Most important, they need to give crystal-clear guidance to the Justice Department, the lower courts and Congress as to what their new reading of the Constitution requires. The justices dropped the Blakely bomb and then, apparently oblivious to the turmoil they had created, promptly went on vacation. Outside of the ivory tower, however, lower courts need to know how to handle the thousands of cases the justices have cast into doubt. Prosecutors need to know how to render indictments. And Congress needs to know whether it should tinker with the guidelines or whether it has to rewrite the rules from scratch.