MIKHAIL GORBACHEV is back in the Kremlin again. But during his forced absence, the seat of power has moved down the Moscow River to Boris Yeltsin's "White House."The stunning hard-liner coup in Moscow and its equally dramatic collapse have already indelibly altered the Soviet political map. Mr. Gorbachev returns as a man betrayed by his own ministers and generals - the very men he put in place - who first covertly and finally overtly opposed his reforms. Mr. Yeltsin now stands as the uncompromised and unquestioned leader of democratic and economic reform in the Soviet Union, lauded around the world for his courage. By losing, the conservative Communists and their military and secret police allies may have sped up the prospects for change. The democratic forces, led by Yeltsin, now gain momentum. Gorbachev's practice of maneuvering between reformers and conservatives has lost all context as well as credibility. It remains to be seen what kind of Gorbachev the Soviet people will now see. Will, for example, Gorbachev move resolutely to sweep out the institutions, such as the KGB and the Interior Ministry, which spearheaded the coup? How will he reorganize his own cabinet, whose leadership formed the core of the eight-man junta? And will Gorbachev remain the head of the Soviet Communist Party - the organizational base of the coup plotters? In the days ahead the Soviet people will be watching carefully for the first signs of answers to these questions. They will also be watching how Gorbachev and Yeltsin reshape their relationship, both in private and in public. But Gorbachev's stance is less relevant now than before. It is Yeltsin, not Gorbachev, who stands as the guarantor of democratic reform in the Soviet Union. Yeltsin seems content to have Gorbachev sit in the post of Soviet president, seeing far more future in being the president of the vast Russian Federation. But it is uncertain whether he will move to assert his newly won power in more open fashion. While there are certainly surprises yet to come in the aftermath of the attempted coup, there is little question of where Yeltsin is likely to try to lead the Soviet Union. The failed coup seems certain to strengthen the shift of governmental authority away from the central administration and into the hands of the governments of the republics. The desperate effort to seize power was prompted by the imminent signing, planned for Aug. 20, of a new treaty of union which would have formalized a considerable republican role. The coup leaders made it clear they considered the treaty tantamount to a dismemberment of the Soviet Union. Ironically, their own actions may lead to the realization of those fears. The treaty was already imbued with a great deal of ambiguity about the precise division of power between center and republic, combining both elements of confederation and federation. There also was no clear agreement on how to handle six of the 15 republics, including the three Baltic republics, who had declared they would not sign the treaty. Gorbachev had indicated in numerous statements that he would seek to interpret the treaty as an agreement to maintain a strong military policy. While he hinted that Baltic and other demands for independence might be dealt with more sympathetically, he also continued to voice hopes that those breakaway republics would see the light and return to the fold. Yeltsin's view, which now seems certain to dominate, was quite different. His vision of the union is confederal, with republics retaining the power to tax and control over their property and resources, and giving to the central government only what they determine it needs to run essential programs. Moreover, Yeltsin has repeatedly stated his willingness to let the Baltics and others go free without a fuss, a view he already embodied in separate Russian treaties with each of the Baltic republics. Some Soviet analysts believe the republics may even seek to redraw the treaty after the coup, strengthening their control over defense and security policy.