"MAXIMUM JOHN" SIRICA, about to retire from the federal bench after a full, rich and colorful career, hardly lived up to his draconian nickname in dealing with the Watergate coverup case defendants. His sentences were moderate and reasonable. And recently Judge Sirica substantially reduced the sentences he had imposed on the three biggies in the coverup case, former Attorney General John N. Mitchell and former Nixon White House aides H. R. Haldeman and John Ehrlichman. As a consequence, all three will be eligible for parole much sooner - Messrs. Haldeman and Mitchell in June, and Mr. Ehrlichman this month (although he is serving a second, concurrent 20-month minimum sentence for his conviction in the "plumbers" case, which would also have to be reduced).

We think Judge Sirica did the right thing. As a precondition of the reduction of the sentences, he received some taped expressions of remorse from the three men. It was nothing that will find a place in the history of great confessional literature, nothing especially perceptive or moving or plausible even, but American justice is not in the business of forcing public confessions. And the mere fact that these three men acknowledged, at last, for the record that they more or less share everyone else's appraisal of what happened - i.e., who dunnit - is something. Nor is there any arguing with the fact that they are hardly likely ever to be in positions to repeat the crimes of which they were convicted, even if they were disposed to do so, which they claim they are not.

The point is this: They have been punished and they have been punished enough. And in this connection one can only try to imagine how that punishment has been intensified by the spectacle of the unimprisoned sage of San Clemente musing on TV (in return for a potful a money) about their guilt and their mistakes and suggesting that, nevertheless, in his own saintly and unparalleled magnanimity, he doesn't really hold against them what they did to his career. Anyone could take a 20-month sentence - but could you take that?

Just in case you think we are picking on Richard Nixon, we ought to say here and now that we don't think he has been the worst offender in this matter, at least on the hypocrisy front. No, he has only been the second worst. First prize, in our judgement, would have to go those great and famous civil libertarians in the Soviet Union who expressed the other day, through their official news agency, Tass, profound displeasure at Judge Sirica's lightening of the Watergate dentences. "By virtually pardoning the offenders, the U.S. authorities again demonstrate their duplicity," Tass complained. But what were the "offenders" offenses? - you have to ask yourself. Wiretapping? Political burglary? Obstruction of justice? In the Soviet Union, government officials get medals for doing the things Messrs. Haldeman, Ehrlichman and Mitchell got sent up the river for.

But never mind. Judge Sirica knew what the crimes were about and what values were at stake. And to some extent he seems to have helped impart that knowledge to the men who committed them. Now he has intervened in the process in an attempt to keep the punishment from being merely vengeful. It's too much to hope that the Russians, or Mr. Nixon, for that matter, will ever get the point of Watergate. But John Sirica has properly concluded that, where practically everyone else is concerned the points that needed making have been made.