For the most part, a dutiful bow, for which Ronald Reagan has special reason to be thankful, greeted the onset of Senate hearings on his INF treaty. This is just as well. The treaty is important less as the great arms control breakthrough the Reagan administration is celebrating -- as arms control it's worthy but modest -- than as the debut of the next, inevitable and harder stage in conducting global politics in conditions of American retrenchment and incipient Soviet-American de'tente.

This treaty has been in negotiation for years, and the Senate was virtually part of the negotiating team. Executive consultation with Congress was thorough enough to make the formal advice-and-consent procedure opening this week something of a superfluous exercise. Bob Dole's quick leap upon the treaty bandwagon says what one needs to know about its prospects for ratification.

The INF treaty, eliminating all Soviet and American medium- and shorter-range nuclear missiles, has no fewer than three groups of supporters. The first would welcome just about any agreement with the Kremlin. The second thinks the terms of this one (especially on unequal reductions to an equal floor and on verification) are sound and applicable as precedents. Those in the third group think that some of the implications of the treaty -- for NATO security and cohesion and for conventional and strategic arms control -- are pretty scary, but either they don't want to embarrass the president by turning the accord down or they are ready to get on to those larger issues.

That leaves the political interest of the ratification debate, such as it is, arising chiefly from the tradition that the late Sen. Henry Jackson established of adding toughening amendments to arms control treaties during the hearings on them.

The INF amendments come in two varieties, one called (by critics) ''killer'' amendments, which would compel the president to renegotiate the treaty with the Kremlin, and the other deemed (by sponsors) ''constructive'' amendments, which issue the president follow-on policy instructions but do not force him to take INF back to the table.

''Killer'' amendments will come mostly from Jesse Helms and the other narrow-gauge conservatives whose stock in trade is to shame Ronald Reagan with reflections of his own old hysteria -- the condition he had to set aside to make a deal with Moscow.

''Constructive'' amendments will come from Dole, Joseph Biden and others, whose early proposals left the secretary of state, in the words of a Post story, ''noncommittal.'' Translation: gritting his teeth at the prospective difficulty of telling the president's ostensible supporters they are making him look bad.

On this score, I have little sympathy for Ronald Reagan. If political justice were the measure, the Senate would not content itself with putting amendments -- either mean ones or gratuitous ones -- on INF. It would throw the treaty back in his face. In his time as a presidential candidate in the 1970s, nobody did more to make life difficult for presidents trying to move treaties through the Senate, and nobody was more irresponsible in doing so. The worst of it is that his attacks on the Panama Canal Treaty and SALT II actually helped elect him president.

Those were, furthermore, good treaties. The Panama accords took off the board a major source of regional and hemispheric inflammation. Had Reagan succeeded in destroying these accords, he would have put an immense extra burden on his own crushingly difficult passage in Central America. On SALT II, Reagan trashed it for no good reason and to bad effect and then, without having the grace or decency to say so, quietly sneaked back to it. A strong case can be made that he would have done much better simply to have accepted SALT II as a useful interim platform on which to build his own subsequent arms control structure.

Not alone among presidents at treaty time, Reagan is given to making eloquent appeals for bipartisanship and the national interest. That is, when he is not accusing congressmen and senators who disagree with him on an eminently arguable regional issue such as Nicaragua of favoring surrender and communism. He should bless his stars that no powerful and passionate demagogue like Ronald Reagan is at hand to kick him around on the INF treaty.