It is dawning only slowly on Washington and the West that suddenly a tremendous opportunity has opened in Moscow to save the Soviet Union, or Russia, or whatever that place is going to be, for democratic reform.

Noting the prospect, a careful person would immediately want to list the usual 42 reasons to be wary, not to expect too much too soon and so on. All of that I am going to stipulate, however, on grounds that caution is already copiously coded into our political radar and that the vital requirement now is to rise above conventional prudence and find the imagination to see large new possibilities.It is widely accepted - it may even be true - that Mikhail Gorbachev has played out his historic role as the patron of change from above. Boris Yeltsin is the man of the next hour. It is not proven that he's a great leader, but he represents the awakening and ever more insistent forces of change from below.

Stephen Sestanovich, from his scholarly perch at the Center for Strategic and International Studies in Washington, and William G. Miller, who follows the Moscow reform scene closely as head of the American Committee on U.S.-Soviet Relations, make a persuasive case. They suggest that Gorbachev's shift to the right in the past six months unleashed a reaction that in turn produced the current Gorbachev-Yeltsin "truce" or "coalition" whose effect is to revive Soviet democrats and decentralizers. The "nine-plus-one" accord of April 23 - nine Soviet republics plus the central union - was the pivot. Yeltsin's imminent popular election as president of Russia and the turnover of the coal mines to the Russian Republic (and their expected early privatization) show the way.

Americans are entitled to some nostalgia at Gorbachev's decline. President Bush gave him the handsome credit he is due the other day in hailing his foreign policy innovations and early domestic reform. What we are not entitled to is absent-mindedness and inattention to the potential of the new situation taking shape in Moscow. There is a real danger of that now.

During the past five years, it has been enough for the West to sit back, watch Gorbachev perform his magical feats and wait for the marvelous fruits of his policy to mature and drop into our laps: the fading of the Cold War, East Europe's liberation, German unification, the opening of Soviet society. The Reagan and Bush teams have done well enough in tracking these developments, but the United States has been in the relatively undemanding position of responding to initiatives and tough decisions taken by others. Consider the sweaty tug of war we have had on the protocol of receiving Baltic visitors - a typical symbolic and relatively trivial issue.

But now comes a period when, to exploit immensely promising but fragile tendencies in the Soviet Union, Washington must decide whether to go beyond these nudges and nuances into bolder assertions of the American interest. There was some plausible reason to put off this decision while Soviet reform was in its initial exciting but tentative and undeveloped phase. But with the prospect of a real political breakthrough, the United States can no longer take refuge in lesser gestures and sideline commentary. Washington is going to be called on to put its money where its profusely professed interest in democracy is.

Jeffrey Sachs, a hot hand in the precocious new specialty of taking command economies market, argues that for a mere $30 billion a year for five years, the West could hope to bring the Soviet Union to the promised land. Condition the aid explicitly on economic and political reform, he says - I would add: and on an absolute avoidance of state violence against peaceful dissent - and offer it up front, right now, in order to have maximum influence in the Soviet debate. The American share would be $3 billion - peanuts.

The tendency to treat the Soviet Union as an adversary, or as a country that will only do the right thing under pressure, lingers on in American thinking. It accounts for the various schemes, small and large, to keep the heat on Gorbachev, including the current notion that we can buy the future with a one-shot $1.5 billion food loan. It's not all bad. But it's a policy tacitly premised on the expectation of the failure, or at most the stingy progress, of Soviet reform.

Events in the Soviet Union may now finally open a vista of far-reaching progress. This is why we need to weigh not just the familiar negative incentives but brave new positive ones. So far the Bush administration shows no awareness of how the stakes may be changing.