UNITED States steps to normalize trade with the Soviet Union, as President Bush is taking this week in his summit with Mikhail Gorbachev, may in the long run do more to rescue the faltering Soviet economy than any "Marshall plan" of short-term aid.To be sure, the Soviet Union has immediate economic needs that the US and other industrial nations should help meet - although, as the G-7 nations indicated in London this month, that aid is more likely to come as technical assistance than as cash. But if the USSR is truly to restructure and modernize its productive capacities, Soviet managers (and foreign investors) must have the prospect of being able to sell products in world markets. The lowering of US tariff and other trade barriers against Soviet exports won't have a marked effect on the Soviet economy overnight. The Soviets have few products, apart from oil, timber, and some other natural resources, that are in demand by Western consumers. Nonetheless, eased trade impediments will signal Soviet producers and foreign partners that a door has been opened, and that the vast US market is available if they are inventive and efficient enough to make their goods competitive. Initially, Soviet products won't be in much demand, and then mainly at the low end of the price and quality scales. But that was also true of Japan, Korea, and other economic "miracles" in Asia. Like the Asians, the Soviets will find that getting into the stream of world commerce has a feedback effect; their products will improve as they are tested against international standards. And like those new manufacturing dynamos, the Soviet Union has a well-educated and technically oriented workforce. It's anomalous that China, a far more repressive country today than the Soviet Union, enjoys normal trade relations with the US, while the USSR does not. Moscow has satisfied the conditions Washington has placed on normalized trade. The Bush administration is rightly acknowledging that the time has come to further the Soviet Union's reintegration into the world economic order by ending its trade isolation.