NOW A SENATE minority has its chance to exact a toll of mischief as a price for letting the country and the world make progress on arms control. The Intermediate-Range Nuclear Force treaty has overwhelming support among the American public. Yet the treaty clause in our Constitution makes it possible for 34 senators to block its passage or hold it hostage to parochial concerns.

Many Americans accept the Constitution's requirement that treaties be approved by a two-thirds vote in the Senate as an essential part of our system of checks and balances. In fact, it originated in 1787 for reasons that have little or no relevance to 1988. Also, it is patently undemocratic; it has had significant and deleterious effects on U.S. interests; and it threatens to have worse effects in the fairly near future if, for example, a strategic-arms treaty is submitted for approval.

As to the treaty clause's historical origins: The excesses of George III had made the framers of the Constitution acutely sensitive on the subject of executive tyranny and corruption. There was particular concern that a president might seek to enrich himself through collusion by treaty with a foreign power. Hence the need for congressional oversight.

The decision to entrust this responsibility to the Senate alone had largely to do with the framers' concept of what the two bodies would be like. A prevailing view was that the Senate would be composed of senior wise men distinguished for their "rank in life and weight in property," who could advise the president as the House of Lords had advised British monarchs since Norman times. The House of Representatives, on the other hand, was mistrusted because of the framers' fear of another form of tyranny, tyranny by the majority. This may sound strange to our ears, so attuned to the principle of majority rule. It must be remembered, however, that the framers were predominantly men of property and that protection of property was one of their dominant concerns.

With memories of Shays' Rebellion of debtor farmers still fresh, James Madison warned his colleagues that, as the country's population grew, power could slide into the hands of the numerous poor. He pointed to the Senate -- a body that was, until 1913, chosen by state legislatures rather than direct election -- as the guardian of property against this unruly spirit. And since treaties often require secrecy, the Senate, with its far smaller membership seemed a safer repository for confidence than the more populous House.

But why two-thirds of the Senate? This seems to have been a holdover from the Articles of Confederation, which contained a long list of actions that the Continential Congress could not undertake "unless nine states assent to the same." But of these, only treaties were made subject to a two-thirds requirement in the Consitution. None of the 1787 reasons for the treaty clause should be persuasive in our own time. Especially anachronistic is the mission of frustrating the majority. Consider that it is theoretically possible for senators representing less than seven percent of the population -- the 17 least populous states -- to defeat a treaty! While it is unlikely that these less populous states would vote in a bloc opposed to all the others, the very possibility is offensive.

The best known instance of the treaty provision's impact on history occurred in 1919, when a Senate vote of 49 to 35 in favor of the Treaty of Versailles fell seven votes short of the two-thirds needed for approval, thus essentially dooming the League of Nations and damaging the postwar organization of the peace. Since World War II, moreover, as a report issued in connection with last year's bicentennial of the Constitution noted, over 40 treaties submitted to the Senate have either been rejected or have never come to a vote. These included three arms-control treaties, several human-rights conventions and a number of boundary, trade, tax and environmental agreements.

Perhaps more important than the effect of the clause on already signed treaties is the fact that it prevents desirable treaties from being negotiated at all. As James L. Sundquist has written: "Every president and secretary of state know that they may go no further in any negotiation than the minority of the day will finally accept." In 1963, for example, President Kennedy ceased pressing for a comprehensive test ban when a head count indicated it would fall short in the Senate.

In other cases, in order to get a treaty through, deals or "killer" amendments have had to be accepted, such as the belligerent military "safeguards" Kennedy swallowed to win Joint Chiefs' support for the Limited Test Ban Treaty. This concession was based on the probably still valid perception that defense-minded elements can muster 34 votes in the Senate against any arms-control treaty they dislike.

There have been a number of attempts to modify the treaty clause. The first came at the Constitutional Convention itself, when a proposal to require treaty approval by a majority of total Senate membership failed of passage by only one vote. The most determined effort came in 1945, when the House, by overwhelming vote, initiated an amendment requiring that treaties be approved by a majority of both chambers. Predictably, the Senate refused to consider it.

The only way to amend the Constitution without Senate consent is by calling a constitutional convention, something many thoughtful people wish to avoid. But it would still be desirable at least to reduce the required margin of approval, preferably to the simple Senate majority that the Consitutional Convention came so close to accepting.

Today, any prospect for amending the treaty provision seems a long shot. But one can at least sow the seeds of future action, to be taken, for example, if a Senate minority again frustrates the popular will on a major issue. In the short run, the overhanging threat of reform might even serve to make the minority less recalcitrant.

Benjamin Loeb collaborated recently with Glenn Seaborg on "Stemming the Tide," a book about arms control in the Johnson era. A longer version of this article appeared in the October 1987 issue of the Bulletin of the Atomic Scientists.