THE SUPREME COURT has come up with a good answer to a difficult and important question. When can a citizen sue a public official personally for violating his constitutional rights? The answer, in Justice Byron White's words: only when the official's actions "violate clearly established statutory or constitutional rights of which a reasonable person would have known." In other words, you can sue a public official personally only when you can show that he violated the letter of the law.

That may seem obvious, but it hasn't been the only view advanced by local courts and angry plaintiffs. The case the court decided was brought against John Mitchell for having approved, as attorney general in 1970, warrantless wiretaps. Many people believed that Mr. Mitchell violated the Fourth Amendment protection against searches and seizures, as the Supreme Court subsequently ruled. But the wiretaps didn't explicitly break the law -- in statutes or Supreme Court decisions -- as it existed at that time. Accordingly, the court says, Mr. Mitchell cannot now be subjected to a lawsuit.

To understand why this is an important result, remember that former U.S. attorneys general are not the targets of most such lawsuits. They are brought more often against officials at all levels of government by litigants who want to make new law. It's unfair and unjust for officials to be subject as private individuals to lawsuits for acts that were, under the letter of the law, legal at the time they were committed. It's also bad government, because it may move officials to shy away from decisions that seem likely to rile litigation-prone constituents.

At the same time, the court's decision does put a burden on officials by making them clearly vulnerable to lawsuits when they have good reason to know their acts are illegal. Officials know now, if they did not before, that they must pay attention to the Constitution. But they also know now something of which they might have been unsure: if they do pay reasonable attention to the Constitution, they'll be protected against the perils of lawsuits that could cost them more in fees alone than their yearly salaries. It is a good result all around.