THE idea of motivating a sales force through commissions based on sales has been used since the earliest days of trade. But did you know that there are 750 United States government employees who currently have to raise most of their agency's budget by selling US weapons in the third world?These are the third-world field staff of the Defense Security Assistance Agency. They work with officials in their host countries to design arms sales requests that will meet both the host government's needs and US political guidelines. Their promotion prospects are closely linked to their success in raising the 80 percent of the agency's budget that comes from a 3 percent levy on sales. In recent years, they have been doing very well. In 1990, they helped sell arms worth $18.5 billion to third-world governments. That boosted the US into first place in the third-world arms-supply league, with the Soviets trailing at $12.1 billion. Then came the Gulf war. Afterward, in his landmark March 6 speech to Congress, President Bush said, "It would be tragic if the nations of the Middle East and Persian Gulf were now to embark on a new arms race." In May, he invited the other four major arms-exporting nations to join the US in exercising "restraint" in the supply of conventional weapons to the Middle East, which is easily the largest arms market in the third world. That was a laudable goal (though it fell far short of the moratorium on arms transfers that some of us advocated). Meanwhile, the actual behavior of US arms-sellers in the Mideast does not look remotely like "restraint." In the five months following war's end, the administration agreed to transfer more than $6 billion worth of arms to the region, according to congressional experts - more than four times as much, in dollar terms, as the US shipped there in 1984-88. What is going on? The global trade in arms has much in common with the global trade in drugs. The drug trade is fed by the ever-growing appetite of recipients, which bears little relation to healthy human needs. In the case of the arms trade, the appetite may start off as an understandable need for community defense, but it can quickly become warped - by exaggerated theories of building "deterrence," by the need to placate the officer class, or by growing local taste for commissions. In the arms trade as well as the drug trade, as the volume of trade increases it creates something like an addiction for the supplier. The economies and social systems of several nations have become warped by the growth of drug exports; the same can be true of arms trade. Is the US on its way to becoming the Colombia of the global arms market? WE should not forget, either, that behind all the fancy "strategic" talk about delivery systems, deterrence, and the rest, the ultimate purpose of these products is to kill and disable people. Third-world governments too often end up using them to do just this, whatever elaborate reasoning is used to justify the sales. Fortunately, the US is still strong enough to pull away from the lure of the global arms trade without too much disruption. The Pentagon has already started notching down its own procurement budget. While this reduction continues, we should not seek to keep existing arms-production lines going by stimulating third-world sales. Given the enormous stockpiles built up in the 1980s, we could still meet our foreseeable defense needs even if we mothballed nearly all the weapons factories. We should tell the industrial conglomerates that have run those factories that they must adapt their energies to productive civilian enterprise. Those are the kinds of industries that we ought to be building up through exports. For starters, please, let's take Uncle Sam's arms-sellers off commission! And President Bush, yes, let's have real arms-sales restraint. Let's tell our friends in the third world that, in this vulnerable age, a nation's security needs are met more effectively by building relationships with former adversaries than by acquiring bigger and better arsenals. After all, your predecessor, Ronald Reagan, led the way in this, with his historic reaching out to the one-time "Evil Empire."