AS THE SEVEN gather in Houston today, they will be greatly tempted to focus their discussions on the collapse of Soviet power in Eastern Europe. This one will be the first of these annual conferences to be held in the heady atmosphere being generated by the end of the Cold War. For the people who lead the seven big industrial democracies, it's a rare moment -- one in which they are riding on the crest of great events. It would be easy to turn Houston into a continuation of the NATO talks last week in London, another stage in the intricate conversations about arms reduction and German unification that will go on through the summer and autumn. But there is other business as well that's got to be taken up at Houston -- business that's much less congenial and more divisive, but equally urgent.

Trade is at the top of the list. One way or the other, either by settling the key issue or evading it, the seven will determine the outcome of the negotiations, now in their fourth year, to strengthen and modernize the rules of international trade. These negotiations are now stuck on agriculture, and specifically on the European Community's bad habit of over-subsidizing its farm production and then dumping its unwanted surpluses abroad. That kind of dumping is illegal when it's done with manufactured goods, and common sense calls for extension of the same discipline to agriculture. If the seven at Houston don't settle it, the whole trade negotiation will collapse, and the rest of the world will conclude, reasonably enough, that the Western Europeans did it deliberately because they are losing interest in world trade -- that they are entirely preoccupied with expansion into Eastern Europe. That suggests a world dividing into closed trading blocs. If the Europeans want the United States to remain interested in Europe, as they say they do, they are going to have to demonstrate it by meeting their responsibilities to an open worldwide trading system.

As for environmental policy, here it's the United States that's on the defensive. The question is not a choice between right and left, as many American conservatives -- particularly those at the White House -- seem to think. After all Margaret Thatcher has now begun to press for serious action. What the seven need is a joint strategy to begin curbing atmospheric pollution in ways that will support economic growth rather than damaging it.

To the extent that the world has a governing, or at least guiding, body, it is the one now on view in Houston. Its decisions on aid to the Soviet Union will have great immediate political importance. But for the longer future it's the seven's attitudes on trade and the environment that are likely to make the larger difference.