THE unsuccessful coup attempt of late August was yet another dramatic moment in the revolution transforming the Soviet Union. Americans are clearly pleased with the recent events, which seem to signify the successful culmination of nearly a half-century of US foreign policy, but they remain cautious about relations with our erstwhile rivals.A majority of Americans is now convinced that the cold war is mostly over and that the Soviet system is changing both economically and politically. Moreover, Mikhail Gorbachev and Boris Yeltsin are both remarkably popular here. In general, the public thinks our government should help (at least in principle) to strengthen the economies of the former Soviet republics and grant "most favored nation" trading status. But whether because of residual animosity, concern about political instability, or doubts about their own economy, Americans are not willing to go much further. Majorities oppose low-interest loans and direct monetary aid. Most people feel that the US is doing as much as it should to help ease the current economic crisis in Russia and the other republics and that we should move slowly until the situation there becomes clearer. At this point, perhaps in recognition of the potential complexity of the post- cold-war world, the public also remains cautious about making major cuts in military spending. American public opinion about the current state of Soviet affairs seems clear: lend moral support and open opportunities for free trade, but be careful when America's own interests are at stake.