In the Soviet Union, the sense of turmoil is accelerating, like a car with the gas pedal stuck. With his abrupt offer Thursday to resign as foreign minister, Eduard Shevardnadze has stunned his old friend Mikhail Gorbachev and shaken the Soviet government, already wobbly, to its roots.

Even in a year of surprises, Shevardnadze's exit provides a jolt of high drama in the careening evolution of the Soviet state. It comes at an especially critical time for Gorbachev, who is feverishly trying to keep the weakened Soviet federation from flying apart. And it injects new turmoil into a governing process that had already gotten miserably bogged down.But Shevardnadze's move may have the most impact in the churning world of Soviet politics, where disorder reigns and no prediction is safe. Coming at a watershed period, with Gorbachev anxiously scrambling to cope with mounting economic and social pressures, Shevardnadze's resignation could trigger a new alignment of Soviet political forces.

One clue to this could be found in his brief, pained speech to the Congress of People's Deputies. In that speech, Shevardnadze warned that continued Soviet turmoil could bring on a dictatorship, and he said he was resigning to protest that possibility.

With this blunt warning, he put himself more visibly than ever in the camp of the Soviet reformers and thereby opposed to old-line Communists who have demanded Gorbachev crack down on disorder. He praised Gorbachev's leadership but urged the deputies to deny him the extra presidential powers he had requested.

This fall, as food lines lengthened in major Soviet cities and perestroika continued to sputter, Gorbachev increasingly appeared like a leader hungering for new answers. Beset on one side by embittered conservatives longing for the old order and on the other by impatient radicals demanding a far faster pace toward democracy, Gorbachev has dithered and balked.

Yet as pressures have grown in recent weeks, he has adopted a tougher tone, threatening police crackdowns to cope with unrest and brushing aside talk of independence for the restive Soviet republics. Unwilling to make the broad leaps that radical officials were urging, he adopted a militant law-and-order stance. This retreat toward the right, by a courageous leader he has long admired, may have been what compelled Shevardnadze's move.

If Shevardnadze indeed was acting to bolster Democrats' hopes against the risk of dictatorship, his move could embolden pro-reform forces in the legislature and in the local councils of such cities as Leningrad and Moscow. By the same token, his warnings could add ammunition to the populist hopes of Boris Yeltsin, president of the Russian republic and a tart critic of Gorbachev's sluggish pace of reform.

Yet the Shevardnadze surprise, with its prospect of forcing hard-liners onto the defensive, could end up working to the advantage of Gorbachev and his hopes for a new union treaty to keep the Soviet state from disintegrating. One U.S. expert on Soviet affairs called the Shevardnadze action "courageous" and suggested that it would help stiffen the resolve of pro-democracy forces against an increasingly resentful right wing.

In terms of Soviet foreign policy, Shevardnadze's departure will be keenly felt. He has been not only a loyal steward of the Gorbachev reform agenda, but an accessible figure with strong ties to leaders in the West. His likely successor, Deputy Foreign Minister Evgeny Primakov, will have to confront a bundle of difficult issues - the Persian Gulf crisis, economic aid, a new treaty on long-range missiles - without Shevardnadze's personal rapport or negotiating experience.

With the Soviet state on the brink of fragmentation, however, this resignation will probably have its sharpest impact on domestic politics. And here it is not unthinkable that the popular Shevardnadze could himself become a rallying point for restive reformers who until now have lacked a credible leader.

Impatient with Gorbachev and unsure about Yeltsin, and with radical city leaders still too inexperienced to command a national following, reform forces could find in Shevardnadze the resolute stands they have been seeking.

How this could translate into political change can only be guessed at. But Gorbachev did say that he had planned to offer Shevardnadze the vice president's position in a revised national executive. If this should come to pass, the onetime foreign minister could shortly find himself the heir apparent - and in commanding position to wield the leadership that in Gorbachev's hands has grown weak and indecisive.

Gorbachev said Thursday that he was deeply hurt by his old friend's hasty departure, and the criticism rings true. But the two leaders apparently talked the episode through later in the day; and, to judge from news accounts, it does not carry the air of a bitter, permanent rift.

Instead, Shevardnadze may have become the one thing Soviet politics so badly needed: a catalyst to jolt stalemated political forces off dead-center. If this proves to be true, Gorbachev will owe Shevardnadze far more than he knows.