The case of Sen. Larry Craig (R-Idaho) is holding the Senate up to almost-nightly ridicule by television comedians, but it will bring true discredit onto the body if the Senate Ethics Committee goes through with an investigation of Craig’s conduct.

The Craig case should be dropped forthwith and the resources of the committee should be devoted to serious matters, notably charges that Sen. Ted Stevens (R-Alaska) had his home rebuilt by an oil executive who has admitted bribing elected officials.

However embarrassing Craig’s conduct in a Minneapolis airport men’s room might be to himself and his colleagues, especially his fellow Republicans, it — even with his guilty plea to a misdemeanor count of disorderly behavior — is not a fit subject for an investigation by the Ethics Committee.

Both the Senate Republican leadership and Craig himself are using the ethics process for their own purposes — the leadership, to pressure him into resigning and Craig, to secure some measure of exoneration and provide an excuse to complete his term in the Senate. However, the Ethics Committee ought not allow itself to be used.

No one has been able to cite a Senate rule that Craig may have broken, largely because there are no written rules or guidelines in the Senate Ethics Manual covering the breaking of laws unrelated to a Senator’s official duties. The Ethics Manual is devoted entirely to issues such as campaign finance, disclosure requirements, conflicts of interest, lobbying, gifts and nepotism.

If the Ethics Committee and/or the Senate were to find Craig guilty of bringing discredit to the body — which we doubt — his conviction would amount to an ex post facto action. On the other hand, were the committee to proceed with its investigation and then find no grounds to proceed against Craig, he would claim it as some sort of vindication that he does not deserve after entering a guilty plea in Minnesota and failing to have it overturned.

A review of Senate disciplinary activities dating back to 1811 shows not one case that did not involve official conduct in some fashion — including the censure of Sens. Benjamin Tillman (D-S.C.) and John L. McLaurin (D-S.C.) in 1902 for fighting on the Senate floor. No ethics investigation was launched even after Sen. Edward Kennedy (D-Mass.) pleaded guilty to leaving the scene of the car crash in 1969 in Chappaquiddick, Mass., in which a young former campaign aide died.

Similarly, of the hundreds of cases taken up by the House ethics committee and listed on its Web site, only a handful involved alleged criminal activities unrelated to official Congressional duties — and all were felonies, including bribery, manslaughter and, in 1838, the killing of one Member by another in a duel.

Sen. John Ensign (Nev.), chairman of the National Republican Senatorial Committee, has gone so far as to suggest that the Ethics Committee hold public hearings into the Craig case — an obvious effort to threaten him with public humiliation. Public ethics hearings have been held on rare occasions in the past — in the ABSCAM probe of the 1980s and the “Keating Five” in 1990 — but open recapitulation of the events in Minneapolis would be beneath the dignity of the Senate, for sure.

If Republicans want to pressure Craig to resign because they are politically embarrassed, that’s up to them. But they should not involve the Ethics Committee in the process. The panel has more important things to do.