THE KEATING Five are accused essentially of having peddled their offices by interceding with federal regulators on behalf of a major savings and loan operator who had given them large political contributions. Now the sixth most senior member of the Senate, Daniel Inouye of Hawaii, has come to their defense.

His argument is a variation on the familiar theme that everyone does it, that this was only normal constituent service on perhaps a grander scale, that vigorous intervention on behalf of constituents, whether contributors or not, was once upon a time regarded as a virtue and indeed the duty of senators and would have been seen in that light here again had not the savings and loan industry gone so spectacularly bust. Mr. Inouye called the five "men of unimpeachable character," suggested they were being made scapegoats and warned the six members of the Ethics Committee sitting in judgment that it was the Senate itself that was on trial, its most fundamental practices and perhaps -- in that the charge is trading influence for contributions -- the current system of campaign finance.

We have little doubt that Mr. Inouye was also representing the Senate, saying in public what many senators think but lack the courage to say except in private, and on some points he is right or near enough to deserve attention. There is indeed an element of scapegoating in these proceedings, and a continuum exists between what was done in this case and what is dutifully done every day on behalf of contributors and other constituents by members of Congress. But it's possible to distinguish between points on a continuum; the fact that acceptable and unacceptable behavior may have common characteristics doesn't preclude judging among them.

Charles Keating was not your average constituent, nor even your average campaign contributor. Nor was this your average intervention. The contributions he gave or orchestrated came to tens of thousands of dollars and for two of the five senators, Alan Cranston and John Glenn, hundreds of thousands. At least three of the five, including the two to whom Mr. Keating gave the most, are liberal or moderate Democrats, while he has been a devoutly conservative Republican. Two of the five are from his home state of Arizona, and one, Sen. Cranston, is from the state in which his savings and loan operated, California. But Donald Riegle's main connection to the case appears to have been that he is the chairman of the Banking Committee. Mr. Keating has made no secret of his motive in making the contributions: he wanted help. The help came notably in a meeting between four of the senators and the chairman of the Federal Home Loan Bank Board, then another between all five and regulators from the field who felt that Mr. Keating was taking his savings and loan onto thin ice. (It subsequently failed, at a likely cost to the government of more than $2 billion.)

Everyone understood what the meetings were about. The clear sense of the regulators was that the senators' purpose was to induce them to back off. Question: Is that wrong, and if the answer is yes, what exactly makes it so? Is all pressure wrong? All pressure on behalf of contributors? Or is it only large contributors, or pressure in certain regulatory proceedings? The line is hard to draw, and some would rather take refuge in an appearance standard: the five allowed it to look as if they had been bought.

But that's too fickle a standard. What was done in this case did not just appear wrong; it was wrong, and the committee can find the basis if it wants to. Mr. Inouye is right, though not quite in the way he meant. The Senate is on trial. If what went on here -- the muscling of a sensitive regulatory agency on behalf of an aggressive political contributor -- is not a violation of its rules, it's hard to imagine what is. Yes, the Senate has a representative function, and yes, it ought to change the system of campaign finance, but that's not all that is required.