INDEPENDENT COUNSEL Lawrence Walsh is right on target. In a speech to the American Bar Association meeting in San Francisco last weekend, the former federal judge now charged with investigating possible criminal conduct in the Iran-contra affair was blunt in describing his responsibilities. His office, says Judge Walsh, is not interested in policy differences but in violations of law, and if there is evidence that a crime has been committed, there will be prosecutions. In a statement that is self-evident but in this case appears to need reaffirmation, he said that the personal popularity of those involved will play no part in determining whether or not to prosecute.

Before the hearings began, some observers were predicting the fall of the president and the conviction of a number of government officials on vague and unspecified grounds. Lt. Col. Oliver North, Adm. John Poindexter and the rest were out of favor not only because they had apparently been conducting their own covert foreign policy but also because they had made a mess of things. Nevertheless, people are not indicted for arrogance or incompetence, for favoring the contras or knuckling under to the Iranians or -- most important -- for being unpopular. Judge Walsh reminded his audience of this basic rule of fairness and of its obvious opposite principle: when public opinion shifts and the targets of an investigation become the objects of popular acclaim, this new status should have absolutely no influence on a prosecutor either.

Judge Walsh and his staff have a responsibility that transcends T-shirt sales and bumper-sticker campaigns. Before the hearings began, Judge Walsh's office deposited sealed boxes of evidence with the U.S. District Court here to avoid complications caused by congressional grants of use immunity. None of these lawyers watched the hearings or read accounts of the testimony specifically so they would not be influenced by the testimony or the congressional and public reaction to it. Their focus is on law violations only; it has nothing to do with the sidewalk photographer props or the rise in Nielsen ratings. Just as no individual should be railroaded because the public finds him obnoxious or inept, no one gets a free ride because he's had a haircut named after him.