NOTHING ILLUSTRATES more sharply, or nastily, the power that still lies in the hands of Lech Walesa than the lengths to which the Polish government is now going to discredit him. Having been forced by the bankruptcy of its rule to release him from internment, it is now reported to have undertaken a smear campaign -- showing allegedly compromising pictures and tapes to church officials. It is a typical trick that fearful police play in the face of a superior moral presence. Using it is a telling confession of weakness.

It has been widely asked since Mr. Walesa rejoined his family how he would walk what he acknowledges is a political tightrope. He might provoke the Polish and Soviet authorities to the extent that they would retaliate against him and the workers he unquestionably still represents. He might proceed so carefully that he would lose the confidence of his constituency, parts of which appear to have been driven by the regime to the very edge of their discretion. Mr. Walesa is more experienced than he was when he became Solidarity's leader two years-plus ago, and he had a year's incarceration to ponder his experience. He has asked for a month to take his bearings. The Polish people hardly need to be cautioned about the delicacy of their situation.

But the regime must walk a tightrope, too, notwithstanding its effort to portray itself as the master of a gradually improving situation. The release of Mr. Walesa has shown there are limits to the repression it can impose -- limits set not so much by the absence of physical resources as by the uncertainty -- or is it the certain knowledge? -- of what the costs of a deeper retreat toward Stalinism would be. At the same time, the restrictions the regime has placed on the Solidarity leader indicate its awareness of the continuing vitality of the free spirit in Poland and of the possibility that this spirit may yet find some new form of expression and sweep the regime away.

We suspect the smear episode will backfire on the regime--not because Lech Walesa is a saint among men but because he has already established his moral credentials in a country that historically pays close attention to them. He has the power of legitimacy: the regime can take his liberty but not his honor. The regime controls "only" -- not to make light of it -- what the Marxists call the apparatus of compulsion. Attempting to smear him, the authorities smear themselves.