UNITED States President Bush descended into the fierce crosscurrents of Soviet domestic politics in the Ukraine yesterday. Yet he managed to avoid taking sides.He insisted that choosing between the central Soviet government of his near-ally Soviet President Mikhail Gorbachev and the aspirations for independence of republics such as the Ukraine is "a false choice." Mr. Bush denounced the tyranny of the recent Soviet past, but also warned against the nationalism and isolationism that caused arguments to break out on the sidewalk in downtown Kiev as his motorcade passed. He urged the Ukraine to sign the compromise union treaty Mr. Gorbachev seeks as a new framework for Soviet federation. But, he said, "We will not try to pick winners and losers in political competitions between republics, or between republics and the center. At the final summit press conference on Wednesday, Bush and Gorbachev showed how far the two have moved past merely relaxing their cold-war competition. They like each other and have begun to help each other. When Gorbachev told reporters the two were summoning a Middle East peace conference in October, he was yoking together the two great powers on an essentially US project. This kind of Gulf-war-style cooperation on regional hot spots is exactly what Bush and his aides had hoped to forge here. When Bush was pressed to comment on the slaying of six Lithuanian guards at a customs house Wednesday by still unidentified assailants - an act that raised concerns about Soviet oppression of Baltic independence - Bush pointedly gave Gorbachev and his regime the benefit of the doubt. "I don't think it's fair to link a border incident [to Soviet policy on the Baltics] before you know what happened," he said. Baltic independence remains one of many formal sticking points between the superpowers, and Bush has made a point of it here. But he was determined not to make the Lithuanian incident any more difficult for Gorbachev than necessary. Both leaders described their relationship in personal terms. Gorbachev spoke warmly about the long talk the two men had while walking in woods outside of Moscow Wednesday morning. He took no offense at Bush's queries about the state of affairs in the Soviet Union, but rather "felt also ... solidarity in this." Gorbachev attributed some progress between the nations to the chemistry of their leaders: "I am convinced that without what we have today in our relationship, ... we could hardly count on everything that has happened in the past year." Bush, in a toast Wednesday night, saluted "a man I respect and admire, a man whose deeds during the past six years have given hope to those who believe, as I do, one individual can change the world for the better." The summit may provide a reminder, helpful for Gorbachev with his domestic audience, that he is the Soviets' passport to the world economy and its finances. On that front, Bush could only help him so much, although with a promise of most-favored-nation trade status and a repeal of export credit-guarantee limits, he pulled out all the economic gifts he could afford. This summit also gave evidence that the drift of this relationship is toward less drama and more routine business. The signing of the historic, Strategic Arms Reduction Treaty was the ceremonial center of the summit agenda. Gorbachev described the two men pondering the question: "We've signed the treaty, and what's next?" The answer, he suggested, was embodied in several joint statements on Central America, Yugoslavia, and the Middle East, all areas where the two superpowers would readily have clashed in the past but now find common interests. Bush spoke about moving away from grand summits to meetings where the two men focus on economics or just talk. This kind of summitry suits the personalized foreign policy of Mr. Bush. Here, as elsewhere, he clearly feels most comfortable using personal rapport to shape a definition of shared interests. But Soviet politics, despite the appearance of greater stability in recent weeks, pose many pitfalls for this approach. The rivalry between Gorbachev and Russian leader Boris Yeltsin is a visible challenge to Bush's diplomacy, reminding everyone that power is now divided here. Bush was clearly discomforted by Mr. Yeltsin's attempt to play up his own private summit with Bush. And the bloodshed in Lithuania suggests it may be impossible to avoid making choices that place Bush and Gorbachev at odds. Though Bush may not feel much warmth for Yeltsin, the Russian leader gently pointed out that they share a common view of the Baltics. "It is necessary to give them a chance to become independent and, if they wish, to secede from the union," Yeltsin said in an interview after their meeting. "Unfortunately, President Gorbachev has a different opinion."