President Bush, who is not known to be a political risk-taker, took a big one Christmas Eve when he pardoned Caspar Weinberger and half-a-dozen other victims of the Iran-Contra witch hunt. The firestorm of reaction, which the White House must have feared, has not materialized. But give it time.

There can be little doubt that the gesture was justified and, in the present climate, courageous: Congress has long been engaged in turning political differences into political crimes, and the prosecution - one might say persecution - of government officials for heretical thoughts had even begun to bother Democrats, on and off Capitol Hill. Small wonder: One of their own will soon be ad-ministering foreign policy; don't hold your breath awaiting new "independent counsels" on the prowl.And there can be little doubt that the gesture was just the right tonic for Judge Lawrence Walsh. This was revealed by the special prosecutor's reaction to the pardons. Walsh fairly exploded in petulance, defying what is called legal ethics by introducing a new and hitherto unheralded subject: Bush's "misconduct" and "criminal wrongdoing" in the matter. Walsh, who has spent $50 million-plus of taxpayers' money to no discernible end, will now fix his guns on the retiring chief executive.

Those who might have wondered about the partisan character of Walsh's inquisition need wonder no more. A tape of his Oklahoma City press conference should be required viewing for satirists, psychologists and political scientists alike. Furious at the "contempt for the law" - that is to say, contempt for Walsh - exhibited by "the past 12 years of the Reagan-Bush administrations," it is sadly obvious what the judge's objective has been.

Weinberger has since revealed that Walsh exerted considerable pressure on him to perjure himself to build a case against Ronald Reagan. Weinberger, of course, declined to do so - and was indicted for his troubles.

Those who might have hoped that the special prosecutor would illuminate darker corners of events have been sorely disappointed. With the exception of Oliver North's famous security fence, no one has been convicted for anything they did in the Iran-Contra affair - and even North's conviction was overturned.

Americans like to talk about bipartisan foreign policy, but there is no such thing, especially since Vietnam. Yet what dis-tin-guishes the Walsh phenomenon from quarrels of the past is the extent to which malice has animated policy. Robert Taft might have nipped at the heels of Dean Acheson, and J. William Fulbright surely sullied Lyndon Johnson. But neither Taft nor Fulbright, as bilious as they were, would ever have framed their differences in criminal terms.

And that is the danger of Lawrence Walsh. Justice Robert Jackson once said that it is one thing for a prosecutor to recognize a crime and seek a suspect to accuse; it is quite another to hold a suspect and go searching for a crime. That is not justice, but government abuse, a hallmark of tyranny unfamiliar to Americans.