MIKHAIL Gorbachev is making a grave mistake in ordering troops into seven separatist-minded republics to enforce the military draft law. He invites confrontation with a volatile age group enjoying deep sympathy in the local population. His move, coming as he struggles to enlist the republics in a new union treaty, can only feed the prevailing republic view that the center is alien, dominating and coercive. Perhaps the Soviet army demands of Mr. Gorbachev that he prove, by tending to one of its pet institutional interests, his determination to check anarchy and to keep the country whole. If so, he has made a pact with the elements most antagonistic to perestroika and reform. A regime that sends out troops against unarmed citizens is in profound trouble.

But what else, some may say, is Mr. Gorbachev to do? Is he compelled to allow disintegration in the name of an ideal of ethnic self-determination that many far freer governments shrink from embracing themselves? If he is smart and thinks long-term, yes. Such is the artificial and forcible way in which czars and commissars put together the internal Russian and then Soviet empire that there may be no way left to preserve it that is consistent with the democratic and separatist currents born of glasnost. The best hope for binding up some of the parts is for the center to let go and then to rebuild where possible on a foundation of mutual choice and self-interest. It would be a turbulent process -- but not so bad as what can be expected if Mr. Gorbachev confirms his current course. There is no longer a crouching Germany or Japan, a Sino-Soviet dispute or a Cold War to provide a national-security rationale for evading the task.

Reluctantly, the United States is being drawn into what otherwise would be an internal Soviet concern. It faces requirements of policy and popular pressure to throw its weight, in words, economic aid and diplomatic favor, to one side or another. Given the deep-from-within nature of Moscow's travail, American attitudes cannot make a crucial difference. But with the Soviet Union substantially reduced as a global threat, the United States should not hesitate to weigh in on the side of peaceful democratic change. The White House did this yesterday in a particularly forceful response to the new troop movements. Mikhail Gorbachev first earned broad favor by showing himself a partisan of an enlightened future. He cannot expect to retain favor -- in this country or, more important, at home -- by becoming a partisan of a benighted one.