MOSCOW, SEPT. 29 -- Forget Gorbachev. Forget the gulf crisis. Forget the reunification of Germany. The story preoccupying ordinary Soviets this week was, who is sabotaging the potato harvest?

As a dismal fall gives way to winter -- it started snowing here a week ago -- a bumper potato crop lies rotting in the fields. State food stocks are so low that there has been alarmist talk of hunger and even famine this winter. Together with bread, which also has been in short supply over the last month, potatoes constitute the staple diet for millions of Russians.

In the best tradition of the command-administrative system, crisis management centers have been set up all over the country to "save the harvest." Collective farm chairmen have been issuing desperate appeals to city dwellers to spend their weekends in the rain-sogged fields. The shortage has spawned an abundance of conspiracy theories over who is responsible:

Conspiracy theory No. 1, advanced by Communist Party loyalists and the newspapers they control: It's all the fault of the "democrats." Not satisfied with their election victories in Moscow, Leningrad and several other big cities earlier this year, the self-styled democrats are planning to seize power at national level. Economic chaos is in their interests. The worse things get, the more ordinary people will blame the system.

The most elaborate version of this theory was contained in a Tass commentary titled "Who Needs Rotting Potatoes?" that was subsequently reprinted in official newspapers. The commentary accused radical legislators of plotting a "counterrevolutionary coup" to demand the dissolution of the Congress of People's Deputies and overthrow Gorbachev.

Conspiracy theory No. 2, favored by opposition politicians and the "progressive" press: The Communist system is breathing its last gasps, but the party bureaucracy is unwilling to give up power. The bureaucrats are deliberately undermining the work of the new city councils, hoping that public dissatisfaction will create suitable conditions for an authoritarian backlash or military coup.

Prominent politicians who have signed onto this scenario include the new mayors of Moscow and Leningrad. At a news conference Friday, Moscow Mayor Gavril Popov said that he did not think the conservatives could justify a coup under the present circumstances. But a crackdown might be possible if the hard-liners managed to "provoke serious disturbances, if people are left hungry and without heat."

Despite a good deal of mud-slinging in the media, neither side has yet been able to come up with convincing evidence that its opponents are planning a coup. But the charges and countercharges reflect the tense political atmosphere here as the Soviet Union searches for a way out of its deepening economic crisis.

The tragicomic tale of the great potato shortage is a case study in the difficulties of building a free-market system on the ruins of central planning. Faced with a similar crisis in the past, the authorities would simply have ordered everybody into the fields and told them to start picking potatoes. But citizens' fear of officialdom has vanished, while the incentives of a free market have not yet appeared.

"We have destroyed communism, but we haven't yet built capitalism," complained a commentary in the weekly Moscow News.

Moscow officials say the capital needs approximately half a million tons of potatoes to see it through the winter. So far, only 38,000 tons have been collected -- compared to 279,000 tons at the same time last year. Unless a miracle occurs in the next 10 days, there is sure to be a considerable shortfall.

When it first became clear that the harvest was in danger, Prime Minister Nikolai Ryzhkov resorted to the time-honored technique of declaring a "state of emergency." In a television address, he called for "total mobilization" of the population to deal with the crisis and ordered the army to start picking potatoes. Ryzhkov is widely viewed here as the most influential advocate of maintaining strict controls over the economy during the attempted transition to a free-market system.

The government plan was countered by Popov, an ardent free marketeer, who promised to allow Muscovites to keep most of the potatoes they dug in return for a token payment. Otherwise, he reasoned, the potatoes would rot in the fields anyway. Thousands responded to the call.

Today, in a weekly televised address, Ryzhkov said of the economic situation: "The situation is such in the country now that we must stop the decline. I do not want to dramatize or frighten anyone and I have no right to do so. But we simply cannot leave matters as they are now."

President Mikhail Gorbachev has adopted a centrist position in the argument over how to harvest potatoes -- and, by extension, how to reform the Soviet economy. Intellectually, he seems to recognize that the only way of resolving chronic problems of food supply is to move to a market system as rapidly as possible. But, as a practical politician, he is constantly forced back on the tested methods of running the economy.

In his first use of his new presidential powers, Gorbachev effectively took a step back to the old command economy by ordering factories to extend existing state contracts through next year, even if they were unprofitable. In a recent speech, he seemed almost nostalgic as he recounted how in the old days he had ordered Moscow Communist Party chiefs to drop everything and "save the harvest."

"They said, 'Let's not talk any longer. The party has asked us. We'll do anything.' No questions were asked. They began to divide up roles -- who goes to which district, what money is used, what transport and so on. They took the matter in hand," Gorbachev recalled.

This week, the official press has been publishing reports of Communist Party bureaucrats out in the fields collecting potatoes while the newly elected leaders of the Moscow City Council sit in their offices. "In the best traditions of their predecessors, the democratic authorities are so far feeding their electors only promises," gloated Pravda, the official party newspaper.

Recent opinion polls suggest that the public is divided over who to blame for the shortage of potatoes and other basic food items. A poll published in Moscow News this week said Gorbachev's perestroika reforms are blamed by 12 percent of Soviets, the central planning system by 18 percent, "sabotage by the enemies of perestroika" 33 percent and speculation by the "trade mafia" 36 percent.

A bizarre twist to this week's harvest of conspiracy theories was provided by reports of mysterious military maneuvers in the Moscow region. The army indignantly denied the reports, insisting that the soldiers in question were merely gathering potatoes.