THE ETHICS in Government Act has struck again. A special prosecutor has been appointed to investigate wrongdoing in high places. The republic must be in danger -- or so you would think from the size of the apparatus that has been wheeled in to deal with allegation made against Tim Kraft.

Tim Kraft was campaign manager for President Carter until last Sunday afternoon. He is said to have snorted cocaine in New Orleans a few years ago. Because he was a senior White House aide at the time, that the charge has triggered these events: a full investigation by the FBI, a decision by the attorney general, a request to the federal courts for a special prosecutor, the appointment by three federal judges of a distinquished New Orleans lawyer to investigate further and, presumably, the convening of a special grand jury. To the best of our knowledge, the Marines have not been called in yet, but, then, it's only Tuesday.

All this, unfortunately, is law enforcement according to the book. The well-intentioned but far too sweeping Ethics in Government Act has a trigger so sensitive that a senior official's misstep is likely to bring him face-to-face with the full array of government power. Mr. Kraft will now need to hire an expensive lawyer, as did his colleague Hamilton Jordan a year ago, to defend himself against a charge that is seldom investigated and even more rarely prosecuted by the federal government.

If he used cocaine, as it is alleged, Mr. Kraft should be treated just as are others who use that drug. But he is being treated differently, not just in degree but in kind because it is said he did somethig wrong while holding high office. If the same allegation had arisen in the same circumstances against someone not on the White House Staff, the odds are the prosecutors would have ignored it or, at most, referred the evidence to state officials in Louisiana.

Neither the case of Mr. Kraft -- so far as the present public knowledge of it goes -- nor the case of Mr. Jordan a year ago involved the type of criminal activity people had in mind when the Ethnics in Government Act was passed. That act was designed to guarantee the public that serious charges of serious wrongdoing against major public officials would be fully and fairly investigated and prosecuted. The assumption was -- or so we thought -- that special prosecutors would be mainly concerned with crimes that somehow related to the way a public official had performed his duties. The act grew -- remember -- out of an episode in which high officials were involved in burglary, wiretapping and obstruction of justice. Possessing small quantities of cocaine, a misdemeanor under federal law, does not belong in the same category with such misdeeds.

The use of the special prosecutor device in such minor matters does two things: it opens the way for reckless harassment of individuals in government and it cheapens the law itself. Unless Congress revises the Ethics in Government Act to restrict the kind of allegations that trigger its elaborate processes, the appointment of a special prosecutor is likely to become a routine event that does individuals harm and the public interest no good. Special prosecutors ought to be saved for special cases.