The dangerous knowledge gap between the Bush administration and the Soviet Union's politics of upheaval became obvious with the stunning resignation of Eduard Shevardnadze.

Shevardnadze was the glue binding President Bush in total support of Mikhail Gorbachev. That is weakened by not only Shevardnadze's departure but by his brutally frank warning that Gorbachev's regime is sinking into a "coming dictatorship."

Against that warning from the Soviet leader most respected in the West, not excluding the fading Gorbachev, Bush's plan to send a billion dollars in food aid and technical assistance to a new dictatorship becomes less tenable. An Oval Office taken by surprise by Shevardnadze's action must now review its options.

Sources tie Shevardnadze's decision to events in his native Georgian Republic. But he also is clearly shaken by Gorbachev's new reliance on a power base joining hard-line Communist Party cadres, the military and the KGB-police forces. That may end up devouring Gorbachev himself. Or the hard-liners could use him as nominal leader of an anti-reform, anti-nationalist throwback. That contradicts Shevardnadze's moving words that "the future belongs to democracy and freedom."

Bush's decision only two weeks ago to waive trade restrictions imposed by the Jackson-Vanik amendment and to approve technical aid that requires a formal finding of a Soviet "emergency" was under fire long before Shevardnadze's attack on incipient dictatorship. Sen. Bill Bradley (D-N.J.), the leading Democratic specialist on U.S.-Soviet economic relations, blasted it last week for coming at a "particularly inopportune" time.

If "inopportune" then, it may become unacceptable now. The president's advisers now know that predicting what may happen tomorrow in the shadowy Soviet world is an impossible art. Desperately wanting to prop up and sustain Gorbachev, Bush may be seriously underestimating the rapidity of the decline and fall of perestroika and glasnost. If so, U.S. policy must quickly adapt.

That was the central threat implicit in Shevardnadze's eloquent statement to the Soviet assembly of deputies. "If you make a dictatorship," he said, "no one can say who will become dictator" -- referring to the growing power of anti-reform hard-liners.

Shevardnadze's reasons for quitting all revolve around his central fear that the forces of political repression are gaining ground too fast to be stopped. He knows that his native Georgia will be the first target of the forces of violent repression. Of all the Soviet republics now demanding independence from Moscow, Georgia is where antinationalist violence by Soviet police and military is likely to break out first.

It happened in April of 1989, when Shevardnadze was out of the country. A score of Georgians were massacred in the capital of Tbilisi, killed by gas and sharpened spade-blades. He kept his silence but is known to have been outraged.

All Shevardnadze's family -- his son, daughter and three grandchildren -- lives in Tbilisi. Family roots go back generations. If State Department and CIA estimates are correct that a far bloodier explosion than 1989 may come any day in the seething, Moscow-hating Georgia, Shevardnadze would find himself facing an intolerable choice: quit in rage at the Gorbachev regime or be seen as a traitor to his homeland.

Shevardnadze is also known to have been irritated when Gorbachev sent Yevgeny Primakov on a worldwide diplomatic trip to find a peaceful solution to the Persian Gulf. He thought Primakov was upstaging him, and there were many rumors at the time that Gorbachev wanted Primakov as his foreign minister.

If the circumstance of Shevardnadze's resignation means the United States dare not continue its policy of trying to prop up Gorbachev, it also signals dangerous times ahead for the state of Eastern Europe, particularly Poland. The Polish army has now moved its best troops to its eastern border with the Soviet Union -- to hold back an invasion of refugees, not for a military attack.

The faster the unraveling of the Soviet Union, the greater the fear that millions of Soviet citizens will try to escape to the West. For George Bush, this is a sober moment of recalculation.