THE SPECIAL COUNSEL, Paul J. Curan, did the job to which he was assigned, and he did it thoroughly. He went through the records of the Carter family's peanut business and the tax returns of several of the Carter family, including the president. Mr. Curran and his staff when through the accounts of the banks with which the Carters dealt. The went through the accounts of the Rafshoon advertising agency. The conslusions that this investigation has now reached are entirely persuasive.

Mr. Curran reports that the affairs of the Carter peanut warehouse, from 1975 to 1977, were chaotic. There were "material" errors in the books. Some of the warehouse's money was traced to Billy Carter's service station. There were large and repeated bank overdrafts. The warehouse sold peanuts that it was supposed to be holding as collateral for the loans.

But the key point is that none of the banks' money found its way into Jimmy Carter's presidential campaign. Jimmy Carter was not running the warehouse in that period, and his candidacy did not benefit from the unusual and dubious concessions that the banks were making to it.

The trail of suspicion began, you may remember, with the grand jury investigation into Bert Lance's management of the National Bank of Georgia. The Carter warehouse was a prominent customer of that bank. In view of the close political relationship between Mr. Lance and Mr. Carter, questions arose -- not unnaturally -- about other possible uses and misuses of the cash provided by those very large overdrafts. The result was, eventually, Mr. Curran's appointment last March.

Mr. Curran's report confirms the earlier impression of the warehouse's troubles. The family business began a substantial expansion -- taking out loans for the famous peanut-shelling machine and for a new building -- just as the senior member of the family was opening his campaign for the presidency. That left the management of the business in the hands of Billy Carter, who -- whater his other talents -- is not much of a bookkeeper. That's when the financial trouble started. The National Bank of Georgia complained a little, privately, about the overdrafts, but continued to carry them. After the election, Jimmy Carter put the business into the hands of his trustee, Charles Kirbo, who subsequently leased the warehouse to another operator and paid off all the loans. Mr. Curran said this week that "no indictment can or should be brought against anyone."

The institution of the special counsel, or special prosecutor, has served both Mrs. Carter and thel public well in this case. Rumors of financial scandal involving a president are corrosive, and full investigation is the only way to meet them. But the special prosecutor is not a device that ought to be invoked frequently or lightly -- not, for example, in the case of Hamilton Jordan, the president's chief of staff, and the various accusations that he has used drugs. Those are not charges that reach the basic integrity of the conduct of government. The special prosecutor is an instrument of last resort. Mr. Curran's verdict is not entirely flattering to the Carter family, but it will be reassuring to other Americans.