THE HARD part of the Soviet revolution begins today. Mikhail Gorbachev is to send up to the Soviet parliament his economic reform plan. Previously, he had effectively dismantled the Communist Party, the political mechanism of Soviet rule. Now he is undertaking to dismantle the economic mechanism, the centrally controlled economy. Creating the new market economy is one of the great experiments of the times; it has never been done on anything like this scale. Many Soviet citizens wonder desperately whether it can be done; many others know in their bones it cannot.

Certainly the obstacles are formidable. The old system fell apart before the new was devised, and the existing economy is a wreck. There are deep divisions and confusions about how to proceed. Central authority to impose or even guide a new model weakens by the day. To engage the participation and consent of the republics, the counties, individual factories and even local blocks becomes ever more necessary and arduous. The openness that reform demands is fueling internal divisions and splitting the country on ethnic lines. The threat of disruption up to and including civil war or a coup is widely credited. Accelerating reform, the alternative, inevitably first worsens the condition of the people.

There is, however, an X factor in the Soviet scene: the determination and energy of people who think the country can make it or who are prepared to take the chance. This starts with Soviet President Mikhail Gorbachev, who seems finally to be escaping from discredited doctrine and finding a path to economic reform, and Russian President Boris Yeltsin, a former Communist who is bringing his populist bent to an emerging coalition with his erstwhile patron. Under this pair are advisers of brilliance and courage. Ruled from above and by force, Soviet society had been kept from knowing itself. The problems it now must confront may seem insuperable, but thousands, perhaps millions, of citizens are investing themselves in a solution.

President Bush, having rightly determined that the old Soviet threat to the United States is no more, has offered to be "as forthcoming as we possibly can" to help the Soviet economy. The first large test may come as early as this winter, when for purposes of immediate survival, there may be unabashed requests for quantities of basic supplies -- food, fuel and the like. The longer test will be to use the ideas and institutions of the West to draw the Soviet Union -- or whatever new political forms it may take -- into a growing world economy. This is the uncertain and essential process that formally begins today in Moscow.