SEVERAL MORE senators have now joined the cry for a special prosecutor to look into the affairs of G. William Miller, the secretary of the Treasury. That goes too far. The evidence does not indicate that Mr. Miller committed perjury. But it is necessary to add that the findings of the Securities and Exchanges Commission are not flattering to Mr. Miller.

Two years ago Mr. Miller assured the Senate, in great detail, that Textron, Inc., had certainly not made any illegal or improper payments while he was running it. Mr. Miller was testifying before the Banking Committee at its hearings on his nomination to his previous job as chairman of the Federal Reserve Board. Two weeks ago the SEC charged, in a suit against Textron, that Textron had indeed made extensive payments that went, directly or indirectly, to the officials of foreign governments buying Textron's Bell helicopters. That happened in the period when Mr. Miller headed Textron and, the SEC claims, Textron's Bell division knew "or had reason to know" about these payments. Textron has settled the suit with a consent decree in which it neither admits nor denies the SEC's charges, but agrees to take preventive measures in the future.

Did Mr. Miller know about the payments? After a great deal of investigation, by Senate staff and the SEC, there is no demonstration that he did. The Justice Department, which looked into it, says that he did not.

But should he have known? That's a much more complicated question. For years the business of selling aircraft in the Third World has notoriously been attended by all sorts of irregular payments -- kickbacks, bribes, lavish commissions and, in general, grease. In view of the prevalence of those practices, it is strange that an able and experienced executive, at the top of a company in that business, should be oblivious to these payments. But sometimes people do not know what they do not wish to know -- particularly if that wish is clear to their subordinates.

Mr. Miller was promptly asked at a press conference whether he intends to resign, and of course he does not. Nor does President Carter want him to go. But should he go anyway? No; the case is not compelling.It is a study in shades of gray. If he thought that he was telling the Senate the truth in 1978, perhaps he was guilty of not coming clean with himself at Textron. But a degree of self-deception is not necessarily a disqualification for public office.

As for the special prosecutor, that institution is in some danger of being degraded by overuse. It is a big gun and ought to be reserved for big game. It is properly employed only in matters touching people whose power might protect them from any less extraordinary inquiry. A special prosecutor was rightly appointed, for example, to look into the charge that funds had been illegally funneled through the Carter family's peanut business into the president's campaign. When the special prosecutor found that charge to be false, his judgement carried a weight that none of Mr. Carter's subordinates could have given it.

But the Justice Department does not work for the secretary of the Treasury -- and he demonstrably has no influence over the SEC.