BRUSSELS -- The bribe the West is offering to the Soviet Union for a speedy and smooth German unification inside NATO has become so obvious that spokesmen for all the governments concerned are busy denying that it exists. That is a good sign that the deal on Germany is beginning to close.

The unavowable nature of the bribe (sorry, make that ''aid'') clouds what should be an open and vigorous debate on the terms of this transaction. It creates a phony debate over whether the United States and its allies should play tooth fairy and deposit $20 billion or more under Mikhail Gorbachev's pillow before or after serious reforms in the Soviet economy begin.

That is essentially an economic question. But the West's leaders have a political choice to make. Is throwing $20 billion down the rathole of the Soviet economy a bargain if it produces smooth German unification and final Soviet withdrawal?

Public statements by President Bush and Secretary of State James Baker suggest their answer is no. But what they say privately to some European leaders leaves the impression that their real inclination is to say yes, particularly if they can score a twofer by getting Gorbachev to cut or halt Soviet economic aid to Cuba in return for Western underwriting of perestroika.

Twenty billion dollars for a united Germany is not a bad bribe. But it does not go far enough. In constructing the deal they have in mind, Bush and Baker need now to look beyond the immediate objective they have been pursuing relentlessly and see an even larger picture.

Rarely in the past 214 years has American policy toward Europe been so clearly focused on a single, immediate goal. The United States is no longer simply acquiescing in Chancellor Helmut Kohl's hurried dash to wrap up unification by the end of the year; Washington believes that a speedy marriage of the two Germanys to each other and then to NATO is in American interests. If Kohl were to falter, he would find a heavy American boot prodding him forward.

Baker quickly gave up on trying to nail the German whirlwind to the floor and decided to run in front of it instead. Britain's Margaret Thatcher and France's Francois Mitterrand have now followed in abandoning the stalling positions they had staked out in front of Hurricane Helmut. They accept that the fastest unification is the best unification. They are exacting compensation from Kohl in internal European Community struggles.

The Soviets are coming to terms with the need for a quick resolution on Germany. They will stall, haggle and obfuscate throughout the summer. But like the beautiful woman in Winston Churchill's story who showed interest when offered a gigantic sum for an evening's companionship and then anger when a paltry amount was next mentioned, it is the price, not the principle, that is now under discussion. Circle Nov. 19 on your calendar for an all-European conference in Paris to bless the deal.

Characteristically, the Bush administration has chosen its tactics with brilliance and left bigger questions for later. That is, it is still unclear how the rushed joining together of the two German states will further the strategic goal of the administration of remaining ''a European power, not just a European presence,'' in the words of a senior Bush adviser.

This formulation is a nice summary of America's long-term problem in the new Europe. A power decides. A presence observes. How does America go from enforcing continuity during the Cold War to guiding change in the post-postwar era? Some answers may begin to emerge at the NATO summit in London this week and the Group of Seven gathering in Houston the week after -- if Washington seeks to deal at these summits with the future not only of Soviet-American relations but also of German-American ties.

The White House treats a unified Germany as a wonderful Christmas present that history has left under George Bush's tree. But there is no guarantee that a ticking time bomb does not lie beneath the gay wrapping.

Current administration policies cannot guarantee that united Germany will agree to stay in NATO, keep Allied troops on its soil and continue to renounce nuclear weapons beyond the transitional period for complete Soviet withdrawal.

Granted, the strongly supportive policy Bush and Baker have adopted toward Bonn will make it extremely difficult for Kohl or his successor to look the American president in the eye and say that the new Germany has to go its own way. Making it difficult is the idea.

But nations tend to have short memories when it comes to their vital interests. The United States needs to seek firmer guarantees than it has yet achieved from the Germans. The London and Houston summits offer final opportunities before unification is locked in.

Bonn's desire to get its European, American and Japanese allies to join the economic bailout of the Soviet Union, even though German money will make up most of the aid fund, gives Washington new leverage. Kohl showed in the European Community summit in Dublin that he desperately wants to avoid the appearance of a new Rapallo -- a German-Soviet deal.

A Western economic-aid package conditioned on German as well as Soviet assurances on the future would be well worth considering (translation: a bribe worth giving). It will not ''save'' Gorbachev, since Western aid is simply going to cause the Soviets to put off the brutal economic reforms needed; but it may ''save'' Kohl.