HOW the West must stir itself.The creation of a Commonwealth of Independent States to replace the Soviet Union is an extremely high-stakes game. It cuts the old union out of the governing structure - leaving nuclear weapons and the feeding and clothing of millions in the hands of three or four new and untested nation-states whose economies are reeling. The current joke in Moscow is that there will be no food riots this winter because everyone is too tired. In fact, many Muscovites today get up at 5:30 a.m., stand in a food line until noon, work for a few hours, then go home. That can't last forever. The commonwealth plan could clear up some of the West's confusion over whom to aid - Mikhail Gorbachev, or the republics. United States Secretary of State James Baker III has it exactly right when he says the old USSR is no longer viable. The new plan also means that the West can no longer use the excuse that it doesn't know whom to aid. Pervasive corruption and aid-siphoning will be no less a problem in the republics. But a significant renewed commitment of aid by the West will give Boris Yeltsin and other republic leaders the internal leverage to crack down on such corruption. If the commonwealth plan is high stakes for former Soviet citizens, it is also high stakes for the West. The commonwealth is too big, important, and potentially dangerous for the West simply to stand aside. Both short- and mid-term aid are needed immediately. Mr. Baker should lobby President Bush to rapidly establish consuls in the new republics and teams of on-the-ground investigators who can report back about immediate material needs, as well as the best forms of technical assistance. The question of who oversees nuclear weapons if the commonwealth falls into chaos is sobering. Bush should seize the moment to spend the additional $3 billion needed to dismantle these weapons. The republics want the help; defense spending doesn't get much better than that. Helplessness and chaos are how tyrants rise. The ultra-nationalist Vladimir Zhirinovsky got 6 million votes last June in the Russian Republic elections. Lethargy and neo-isolationism in the West are inadequate for the stormy present in the old USSR.