JUSTICE HAS always been an arbitrary thing -- often to the regret of people who find themselves facing a judge with a reputation for giving long sentences. Now Prince George's and Montgomery have jointed some other Maryland counties in a one-year experiment intended to smooth out the inequities of this arbitrariness. Circuit court judges will use a list of standards for sentencing meant to ensure that crime is equally unrewarding for rich and poor, black and white, in every courtroom. The guide to criminal sentencing ws written by a team of 10 judges under a grant from the National Institute of Justice after a study of 1,800 cases in Maryland courts in 1979.

Under the new procedure, every offense carries a certain grade that is meant to register the weight of the act. A crime committed by an armed person against someone who is handicapped, for example, would be given a higher score than the same act committed by an unarmed person against someone able-bodied. The defendant is also graded on his criminal record: a first offender would get a lower grade than a repeat offender. With the two grades, the judge then computes the sentence that Everyman should receive for a specific crime. Any deviation by the judge must be explained in writing as part of the case history.

The uniformity of such a system has its appeal. But it is also true that there are circumstances that make what appear to be the same crimes committed by comparable people different -- circumstances that also argue for different dispositions of their cases. In addition, with standards for sentencing based on the actual crime committed, it will be more difficult for prosecutors to plea-bargain cases in order to obtain convictions. Juries, too, may react in unpredictable ways; if one considers that standard for, say, rape, too harsh it may decide to acquit a defendant rather than impose a penalty it regards as excessive or unfair.

Are such faults compensated for by the advantages of the free hand that judges are granted to vary from the standard if they have good reason? Supporters argue that this is the key difference between the guidelines being used in the counties and the mandatory sentences that others have proposed.

It is an important difference, and it may be that sentencing standards are the tool that people concerned with increasing crime have been looking for. They can achieve some regularity in justice without losing the benefit of a judge or jury's discretion. The experiment in the counties bears close watching.