Feeling the heat, Mikhail S. Gorbachev has given the Soviet stew another fierce stir. This has mixed up the ingredients, but it's still basically the same old stew, and it won't fix what ails the Soviet Union.

Gorbachev is nothing if not nimble. With his nation's economy in tatters and its political structure in chaos, the Soviet president had been hounded by demands that he resign. But this week he bounced back and managed to strike a deal with heads of the main Soviet republics, including his rival Boris Yeltsin, which offers his troubled nation yet another formula for sharing political power.This makes for exciting political theater, and it will buy time for Gorbachev while his critics, thrown off balance by this latest turn of events, try to puzzle out what his new gambit really means. Even so, this maneuver appears unlikely to make much long-term difference, because it fails to address the core of the Soviet crisis.

Magic Mike has engineered some notable reforms during his six years in power, but he always ducks in the clinches. He has repeatedly balked at chances to take the giant steps needed to achieve democracy and economic freedom.

Last year, for example, he commissioned a "500-day" plan pointing to a wide-open free-market economy, but then junked it as too extreme. He talks incessantly of "new thinking," but still has not seriously challenged the Communist Party's dominant role in national Soviet politics. The problem lies with the system itself. Until his country makes a clean break with its deadening past, no amount of marginal tinkering is going to clear the air.

This having been said, it is also clear that Gorbachev managed this week to fend off his sharpest critics and regain some of his lost initiative. For the time being, at least, he remains the principal figure to be reckoned with.

For one thing, he seems to have convinced leaders of the nine major Soviet republics that he still represents the nation's best hope for surviving more or less intact. A trade was struck: Gorbachev bowed to the republics' demand for greater power-sharing, in return for which he apparently secured their pledge to support a nationwide union treaty.

The most significant compromise, however, was that reached between Gorbachev and Boris Yeltsin, president of the giant Russian republic. After months of mutual sniping, they agreed not only on terms of the power-sharing pact with the republics, but also on a new plan to aid the nation's crippled economy.

Regardless of how such schemes evolve, this agreement sows the seeds for a working Gorbachev-Yeltsin coalition, which many Soviet reformers see as the nation's best chance to head off a worsening crisis. Gorbachev holds political power at the center; if the broadly popular Yeltsin can also attract support from pro-democracy leaders in such cities as Moscow and Leningrad, it could jolt the national Soviet leadership toward real reforms.

At present, however, none of this may be able to combat the nation's immediate emergency. The Soviet economy is crippled by chronic shortages, price increases, inflation and strikes involving more than 300,000 miners. Citizens, freed by glasnost to speak their mind, are taking to the streets in angry protests. Six of the 15 Soviet republics have demanded independence and are busily shaping plans to break away from the union. In some outlying republics, such as Georgia, sporadic violence has stirred concern of possible civil war.

Set against this kind of turmoil, all of Gorbachev's pledges - including a new constitution and new national presidential elections - may not count for much in the end. Tinkering on a grand scale is still tinkering. From every side of Soviet life the president is being reviled as ineffectual, and there is no guarantee that he can deliver on his promises.