Gorbachev is sinking. Who will come after him is unclear. George Bush and James Baker, take note.

The reason Gorbachev is sinking is that he has no popular mandate, and the blame for the Soviet Union's deepening crises is more and more being placed on him. He has taken near-dictatorial powers, but he cannot use them effectively. His authority is evaporating in the clouds of his increasingly frenetic and contradictory speeches.

To put this in perspective, let me stress: for the past four years, Gorbachev has been in part directing, in part presiding over momentous developments that historians will surely see as crucial to the emergence of the U.S.S.R. from the nightmare of communism. Marxism-Leninism and the Communist Party's authority have been effectively destroyed. The command economy has been severely undermined. Democratic institutions and a multiparty system are beginning to emerge. Secession by union republics is ever more widely acknowledged as likely to occur. The outlines of a civil society are gradually appearing. Tensions with the outside world have been sharply reduced. And the virtual impossibility of Soviet interference in Eastern Europe's revolutions has wisely been acknowledged.

At the same time, however, the previous authority of the party has not been picked up by any other institution. Politics are polarizing, making the Gorbachev political center weaker by the day. The economy is foundering in the deadly quagmire between centralization and the market, and social disintegration is gathering pace as crime and ethnic antagonisms spiral upward.

In theory, the new political system that is emerging could gradually gain legitimacy and guide the country through turbulent times without coups or mass violence. In practice, the new legislature in Moscow has proved to be primarily a forum for the pressing of the local or institutional interests of deputies. It has not been a cohesive deliberative body that can assist Gorbachev by debating constructively how to deal with the massive problems the government confronts and by effectively controlling the executive. Recently its chances of building solid authority have been further reduced by Gorbachev's "confiscating" some of its powers and giving them to the powerful new executive presidency -- himself.

Why did Gorbachev feel the need to do this? Because, I believe, he hoped the extra powers would compensate for his lack of a popular mandate. Earlier this year he could have sought such a mandate by holding a popular election for the new presidency. As in March 1989, however, he declined to face the voters -- this time probably out of a justified fear that he could easily have lost in a genuine contest -- against, say, Boris Yeltsin.

When the congress voted on the single candidate for the new presidency, Gorbachev, only 59 percent of its members supported him. By contrast, 96 percent had voted him into the chairmanship of the new Supreme Soviet in May 1989. Even the 59 percent figure probably exaggerates the level of firm support for him in the congress on most issues. He "bought" some of these votes from Baltic deputies in return for promises to help them gain more Baltic autonomy. Also, it seems likely that many indecisive centrist deputies voted for him because they allowed themselves to be convinced that only a "strong hand" could address the country's problems. But if he fails in this, as appears inevitable, their support could easily fade.

Within the party, too, Gorbachev's authority is declining. When elected to this July's party congress, he polled only 61 percent against an unknown opponent. And on May 16, when Pravda printed the impassioned letter of a longstanding party member expressing her disillusionment with him, it attached a curiously weak editorial rebuttal. Who was behind this publication?

More important, perhaps, military leaders and veterans have been denouncing Gorbachev's policies with growing self-confidence, forcing him to curtsy increasingly often in their direction. Also, the KGB is clearly split between his supporters and opponents. Presumably it was the latter who, on May Day, failed to warn him that many of the demonstrators were carrying placards critical of him and his policies. At first he was nonplussed, then he slunk off the Lenin mausoleum. Over the next two weeks he revealed how thin-skinned he was by denouncing the demonstrators as "rabble" and claiming, implausibly, that they had planned to "storm the Kremlin."

Even before this landmark event, Gorbachev had shown symptoms of a growing bunker mentality. For example, he pushed openly for passage of a law penalizing, with up to six years in jail, the insulting of himself. Now, in watered-down form and after much opposition, the law has been approved.

Gorbachev is also jumpy about the emergence of rivals with a popular mandate, especially Boris Yeltsin. Though besieged by issues of party and state, on three occasions in the past two weeks he has devoted large chunks of time to lobbying for rejection of Yeltsin's candidacy for the presidency of the Russian Republic.

The bottom line regarding Gorbachev's standing has been put clearly by Leonid Abalkin, deputy prime minister for economic reform. A month ago he pointed out frankly that the Soviet Union could not embark on the Polish type of reform, because that would require strong political authority -- something the Polish government had, and the Soviets government did not.

In the current situation of deepening chaos, the only optimistic scenario for the future requires the emergence of a president and a legislature with strong popular mandates. If the present legislature were to express no confidence in Gorbachev, and he retired, such a scenario -- peaceful revolution toward democracy and the market -- could possibly unfold. But this seems improbable. Too many strong and divergent forces are gathering momentum. If Gorbachev survives for another year, he will be doing well. At present the Yeltsin left has the best prospect of taking power. It would probably be well disposed to the West. But in a year or two a vengeful right could well have improved its position. In any case, mounting anarchy, then great upheavals, seem all too likely.

We should do what business we still can with Gorbachev. But he may now behave unpredictably, and all agreements with him should take account of the likely future of his country.

The writer is a professor of political science and international affairs, and a member of the Institution for Sino-Soviet Studies, at The George Washington University.