WHEN President Bush arrives tonight in Moscow he will find an apparently rejuvenated Mikhail Gorbachev.Only a few months ago, the Soviet president seemed on the edge of political demise. The restive republics, led by Russia and its populist leader Boris Yeltsin, were threatening to dismember the federal state. At the same time conservative ideologues were demanding Mr. Gorbachev's removal as head of the ruling Communist Party of the Soviet Union (CPSU). Now Gorbachev has an agreement on a new treaty of union with the republics virtually signed and sealed. And the Communist Party Central Committee voted on Friday, after a relatively calm meeting, to accept a new program that repudiates Marxist-Leninist ideology in favor of social-democratic reformism. But to a considerable degree, Soviet observers say, these perceptions are illusory. The agreement with the republics is still not complete. And there is very little consensus in the CPSU other than the desire not to lose power. The all-day attempt to complete the negotiations on the draft treaty of union last Tuesday fell short of the mark. The Russian and Ukrainian governments, which between them contribute the lion's share of Soviet taxes, refuse to have any direct federal tax collection. They will contribute the money they feel is needed to finance federal programs, but at their own determination. According to Ivan Laptev, head of the Soviet of the Union, one of the two houses of the Soviet parliament, a compromise has been worked out in which a joint center-republican body will determine what the money is used for, and on that basis republics will pay a fixed percentage. But no Russian or Ukrainian official has confirmed such a deal. Moreover, such a compromise signals that Gorbachev survives as the leader of the Soviet Union only by ceding a tremendous amount of power to the republics. The day Mr. Bush arrives, Russia will sign its own treaty with the Baltic republic of Lithuania, a republic that refuses to sign the union treaty. "The timing of this event," wrote Izvestia commentator Stanislav Kondrashov last Friday, "testifies to the desire to demonstrate to the President of the United States ... that his major interlocutor in Moscow does not control completely the schedule of events nor even the events themselves." Bush will carefully weave his way around this reality. His schedule calls for him to spend most of his time with Gorbachev, a man he clearly feels comfortable dealing with. But he will also see Yeltsin and, perhaps more importantly, will spend a day in the Ukrainian capital of Kiev. The events at the party meeting may be even more difficult for Bush to comprehend. Gorbachev presented what is unquestionably a radical departure from even the version of perestroika (restructuring) agreed to at past party gatherings. The draft party program explicitly abandons the doctrine that divided the communist movement founded by Lenin from the mild socialism of the German Social Democratic Party and similar European movements. "The model that has been imposed on the party and society for decades has suffered a strategic defeat," Gorbachev said in his closing speech on Friday. "It follows from this conclusion that we have come to face the necessity of a new drastic change of our entire viewpoint on socialism." But almost all the speakers who rose during the two-day gathering shared the views of men like Leningrad party boss Boris Gidaspov, who assailed the draft program as "another step, and a big one, to the ideological and organizational weakening of the communist movement." Yet the party leadership voted overwhelmingly to accept the draft, though it will be amended somewhat in the next two weeks before being presented to the party membership and to a party congress at the end of the year for final approval. How does one explain why the largely conservative party bureaucracy voted this way? "Because their armchair is more important than the program," answered Alexander Yakovlev, former ideology chief of the party and one of the chief architects of Gorbachev's reforms, speaking to a small group of journalists Saturday. Mr. Yakovlev, who stepped down Saturday from his last official post as adviser to Gorbachev, is a leader of the new liberal Movement for Democratic Reforms. Yakovlev dismisses the idea of a right-wing move to split the party. "The right-wingers will accept everything because they are losing ground," he says. But on another level, Yakovlev suggests that this agreement was a tactical move. He points to the fate of the policies adopted last summer at the 28th Party Congress. "There were a lot of democratic and progressive things, but nobody was going to implement these resolutions. The same thing will happen to the program. They will vote for it, but they will pursue a different policy." Yakovlev says it is too late to reform the party. "It doesn't matter anymore," he says. "The train has left the station." But the party retains power over the KGB, the Army, and other security organizations, Moscow News analyst Lyudmila Telen wrote last week. "The CPSU remains a state structure rather than a party and gives orders to a powerful apparat of coercion."