MOSCOW, DEC. 16 -- In the tense political struggle between the Soviet republics and Moscow, President Mikhail Gorbachev has turned decisively to the national institutions of the KGB, the army and the Communist Party as a means of defending central authority.

With the Congress of People's Deputies opening Monday what promises to be a dramatic 10-day session, Gorbachev is expected to press for a stronger presidency and at least preliminary endorsement of a new Treaty of the Union. He undoubtedly will come under fire from the liberal minority, which fears increased authoritarianism, and from conservatives who blame the current economic disintegration on a power vacuum.

According to a high-ranking official in the Communist Party Central Committee, Gorbachev has taken only a temporary rightward tack "to get us through the winter." The official said that only local party organizations, the KGB and the military have the ability on a national scale to crack down on economic corruption and ensure the delivery of food supplies.

But Soviet analysts are wondering whether this strategy is truly temporary, and whether Gorbachev may be risking the momentum of reforms in the name of saving them from disorder. How, they ask, can he make common cause with the pillars of the old Stalinist state and then expect to distance himself from them when, and if, times get better?

"What's the forecast?" asked Russian lawmaker Yuri Ryzhov. "I think there will shortly be an attempt to introduce forms of presidential emergency rule all over the country, or at least in some areas. This is already being done in fact. The tightening of the screws has already started."

In recent weeks, Gorbachev has authorized Defense Minister Dmitri Yazov to warn that the military would use its arms against nationalists who attempt to cut off supplies to regional bases. KGB chief Vladimir Kryuchkov, meanwhile, issued a stinging denunciation of "anti-Communist" forces who challenge Kremlin authority. As Kryuchkov put it in a speech, "To be or not to be, that is the question for our great power."

Gorbachev has issued decrees contradicting attempts by legislatures in the republics to win control over their own economies and political institutions. He also has made stinging attacks on the Baltic states and expressed his opposition to private property, a principle that many Western and Soviet economists believe is indispensable to the creation of a healthy market economy.

Many analysts and legislators here express conviction that Gorbachev is not merely shifting course for the political season, but has instead decided that he cannot tolerate a smaller Soviet Union or one that operates as a decentralized confederation.

"This is not merely a matter of getting through the winter. There is an open conflict now between the republics and the center, between the democrats who are trying to gain power and the traditional institutions of the centralized state which are trying to hold on to theirs," said Andrannik Migranyan, an influential political scientist.

"Gorbachev knows that the KGB, the military and the party are still in place, and he must satisfy some of their grievances, make alliance with them, in order to rely on them," he said.

The latest Moscow News offers a large cartoon of Gorbachev trying intently with needle and thread to stitch together the endless fissures in the map of the Soviet Union. The image seems an accurate reflection of Gorbachev's urgent desire to win approval for a new union treaty.

Liberal deputies such as Galina Staravoitova say that one or two years ago Gorbachev's draft treaty would have gotten wide support as a means of compromise between Moscow and the republics. But since March, the various national movements have accelerated, and every republic in the union has passed declarations of either independence or sovereignty.

The Baltic states, Georgia and Moldavia have already said they will not sign the treaty, while Russia, Kazakhstan and other republics have expressed reservations. Only two Central Asian republics have said they would sign the treaty.

Late to react, Gorbachev is now determined to act firmly. In the Baltic states and elsewhere, political leaders are concerned that he may go even further than his recent decrees, declaring extraordinary powers in their territory or even temporarily dissolving their legislatures.

Gorbachev's actions in recent weeks -- especially his appointment of Boris Pugo, a hard-line former KGB officer, to head the country's law-and-order establishment as interior minister -- have worried the Balts.

But these moves toward a crackdown have won Gorbachev obvious credits with the biggest conservative bloc in the congress, the Soyuz faction. They had been threatening to call for Gorbachev's resignation at the congress if he did not take "decisive" measures to tighten law and order. They voted overwhelmingly this weekend to support him.

A Communist Party official said Gorbachev was badly shaken by conservative criticism at a plenary Central Committee session last week and a recent meeting in Moscow with the heads of state enterprises. The factory directors reportedly were especially hard on Gorbachev, accusing him of letting leaders of the republics run roughshod over him and weaken the links among suppliers and distributors.

Clearly, the Gorbachev era has long since moved into a phase far different from the one characterized by the euphoria of new freedoms won in 1988 and early 1989. Gorbachev says he is not interested in dictatorship. "If I wanted that, why didn't I just begin like that in 1985?" he said recently. But he clearly feels that he risks losing control of the country unless he takes a firmer line.

"When you are facing an economic collapse . . . you have two options," said Estonian Foreign Minister Lennart Meri. "The first is the long and difficult rebuilding of a free-market economy, which is the cornerstone of a parliamentary democracy. Then there is the shortcut. The temptation to rule with an iron fist is especially tempting in a place like the Soviet Union, where there is almost no tradition at all of democracy."