IT IS SAD to see the awesome mechanism of a special prosecution wheeled out for purpose of investigating whether presidential adviser Hamilton Jordan did or didn't snort cocaine in a New York disco in 1978. That is not the kind of misconduct by a government official the counry had in mind when, in the aftermath of Watergate, people hailed passage by Congress of the Ethics in Government act.

Yet neither Attorney General Benjamin R. Civiletti nor the judges who appointed the prosecutor believed they had any other choice. Although the act Mr. Jordan is said to have committed is a misdemeanor seldom presecuted and less frequently even investigated by the federal government, it is a violation of federal law. And under the ethics act, the naming of a special prosecutor is required when a high official is alleged to have violted anyh law, unless the attorney general finds the allegation to be frivolous.

Mr. Civiletti said he could not make such a finding because some sitnesses refused to talk to him. Their evidence, it appears, is the only possible material that could implicate Mr. Jordan, and they have refused to provide it without a guarantee of immunity against prosecution, a guarantee Mr. Civiletti could not give. Everything else the FBI has turned up in its 90-day investigation seems to support Mr. Jordan's claim that he did not use cocaine in the disco. s

A less-strict-minded attorney general might not have read the ethics act so literally. It would have been fairly easy -- and it must have been tempting -- to dismiss as insubtantial whatever evidence the uncooperative witnesses are holding back and to conclude that the original allegations are suspect because of the context in which they arose. They were made, after all, during plea-barganing discussions by two big-time tax evaders.

By taking the careful course that he has, Mr. Civiletti has avoided any possibility that the Department of Justice will be charged with favoritism. The special prosecutor's job is essentially to get the information Mr. Civiletti has not been able to get and then to decide what to do with it. It should be kept in mind that Mr. Civiletti also asked the special prosecutor to determine whether the original informants deliberately lied about the whole affair.

However this new investigation comes out, the burden Mr. Jordan must continue to bear is heavy. We ourselves believe that the weakness of the law is illustrated precisely by the way in which its trap has sprung on Mr. Jordan. That he has decided to stay in place, despite the personal discomfort and financial costs of fighting the charge, is reassuring news. Guilty or innocent, the temptation would be to resign when such an "embarrassing" burden was loaded onto a president's assistant. But there is a terrific political and social cost to everyone -- not just the principals -- when people can be driven from public office by unsubstantiated allegations of wrongdoing. And that, even after 90 days of investigation by the Department of Justice, is still the only kind of allegation that exists in the Jordan case.