To rescue its economy from disaster -- and to qualify for significant hard cash from the West -- the Soviet Union must let the forces of the market work, even if a cold-turkey approach leads initially to skyrocketing prices and heavy unemployment.

At least, that is the conventional wisdom of those experts who recommend shock treatment to convert the Soviet command economy -- and the old Warsaw bloc economies -- to something closer to capitalism.

But Prof. Padma Desai, a member of Harvard University's Russian Research Center, dissents. Desai, in a postscript to a new edition of her study, ''Perestroika: Retrospect and Prospect,'' has no argument with the proposition that the only hope for perestroika is through privatization.

She departs from some other analysts, however, in her insistence that ''This is an inevitably slow process and {is} increasingly seen to be so everywhere, even in fast-moving Poland.'' In contrast to the monetarist approach that focuses narrowly on price stability, she leans to the broader view: Growth and the maintenance of employment must be targeted as well. Clearly, that also seems to be the sentiment of leading Soviet reformers anxious to move toward capitalism.

As John Hart, Soviet expert at the Congressional Research Service, put it: ''Some {Eastern Europeans} have been finding that they are worse off under democracy than under the old bums!'' There has to be a better way.

The issue is of great importance as the International Monetary Fund quietly sets in motion a study of how best to help the Soviet economy. The IMF study was commissioned at the Houston Economic Summit in early July as a compromise between American reluctance to advance cash to the Soviet Union now, and the eagerness of West Germany to do exactly that.

The IMF was directed to consult with World Bank and Organization for Economic Development officials and come up with recommendations by the end of the year.

The IMF has a reputation for a hard-nosed approach stressing price stability and budget- balancing in most situations where it is lending money to troubled economies. But an initial exploratory session with private experts on Soviet affairs suggested to some present that the agency is keeping an open mind. All those attending were impressed by the fact that IMF Managing Director Michel Camdessus sat through the entire meeting, taking notes and asking questions.

Desai argues that ''If the IMF wants a feasible program in the Soviet Union, it will have to make exceptions to its traditional methods.'' A first comprehensive reading on the IMF's approach is likely to surface in a Senate subcommittee hearing early in October. Many members of Congress are concerned that ''reform'' efforts in Poland have already been too severe, reducing production and piling up the jobless totals. And there's no visible safety net, as Polish authorities had promised.

Desai told me that the go-for-broke approach, buttressed with macho metaphors like ''crossing the chasm in one leap,'' won't work in the Soviet Union. And even in Poland, she says, the sharply rising rate of unemployment shows what happens when the monetary brakes are slammed on hard in an effort to control inflation.

''A social contract on wages is absolutely essential during the transition to a market system, if not beyond,'' she says. In the case of the Soviet Union, she anticipates that Gorbachev must find ways of persuading miners and other workers that if they accept wage restraint, job losses will be less severe.

One of the carrots Gorbachev could offer would be a commitment not to let essential consumer-goods prices soar out of sight. That could be done, while avoiding the disappearance of those essentials, she suggests, under a ''dual-pricing'' system, used in India and some other South Asian countries.

This would require the rationing of a minimal basket of consumption goods, including meat, bread, sugar and cooking oil, through state ''fair price shops.'' Everything else would be bought and sold in unregulated free markets. Instead of trying to break up the ''de facto natural monopolies'' in the Soviet Union, such as the giant machine-building plant, Desai for the time being would control their prices and look for competition later. Last week, Gorbachev eased the way for Soviet entrepreneurs to build factories.

Desai is mostly on the right track. The transformation of the command economies into a market system is a huge undertaking. And as Hart points out, the biggest risks probably occur at the beginning when politicians have to deal with the accumulated disaster of the past, as well as the lack of infrastructure and mechanisms with which to make democracy work.

That's why it can appear that giving up the old system makes things worse. That's why the IMF should recommend minimum subsistence levels, including assurance of traditional foods -- such as bread in the Soviet Union. It's a daunting task, but Soviet and East Europeans have to be given options less painful than biting the bullet.