MOSCOW, DEC. 23 -- President Mikhail Gorbachev appears to have chosen the small republic of Moldavia as the testing ground for a new, more authoritarian approach to dealing with the Soviet Union's political and economic crises.

For the last year, the Soviet leader has watched impotently as one Soviet republic after another defied Moscow by asserting the supremacy of its own laws over those passed by the federal legislature. Tweaking the Kremlin's nose has become a national sport, as republics, districts and even individual towns solemnly issue their own declarations of sovereignty.

Under heavy pressure from hard-liners in the Communist Party and armed forces to introduce a strong-arm regime, Gorbachev evidently has decided that the time has come to show who is boss. In a nine-point presidential decree that was given top billing in the Soviet media this weekend, he ordered Moldavia to fall into line behind the Kremlin within 10 days -- or face the consequences.

A republic of 4.3 million people bordering on Romania, Moldavia is a good place for Gorbachev to test his newly acquired arsenal of extraordinary presidential powers. The Russian and Turkic Gagauz minorities resent the ethnic Romanian majority and can be relied upon to support Moscow in a showdown. The Romanian lobby in the United States is not particularly influential -- in contrast with the Balts, who are persistently raising a fuss.

At the same time, most of the Soviet leader's complaints against Moldavia could as well apply to the Baltic states or Georgia in the southern Transcaucasus region. By insisting that Moldavia repeal or revise a whole series of objectionable laws and decisions -- including the creation of a republican guard, a language law that gives preference to Romanian speakers and a proclamation denouncing Moldavia's annexation by the Soviet Union in 1940 -- Gorbachev is in effect setting a precedent for similar action elsewhere.

"Of course, this is all very worrying," said Endel Lippmaa, a senior Estonian official, in a telephone interview. "We have to seriously consider the possibility that the Baltic states will be next."

Unnerved by Gorbachev's apparent shift toward the conservatives, Lithuanian President Vytautas Landsbergis called this weekend for active resistance to any attempt by the Kremlin to introduce "overtly occupationist rule in Lithuania." He told a meeting of the Lithuanian independence movement Sajudis in Vilnius that there are signs that "this kind of rule is already being introduced surreptitiously."

The sense of alarm felt by republican leaders has been heightened by the resignation last week of Soviet Foreign Minister Eduard Shevardnadze and his warning of "approaching dictatorship." In a speech to the Congress of People's Deputies Saturday, KGB chief Vladimir Kryuchkov effectively rejected Shevardnadze's repeated insistence that all conflicts be resolved by exclusively political means, suggesting that it was necessary to counter force with force, even at the cost of blood being spilled.

Rejecting Shevardnadze's charges, Gorbachev said his aim is not to build a "dictatorship" but to create a "strong power." The distinction is significant, because it implies that the president plans to use legal and constitutional means to assert his authority. If Gorbachev resorts to strong-arm measures, he will do so in the name of defending his perestroika program of restructuring rather than ending it.

Recent constitutional amendments and a new law on states of emergency give the president exceptionally broad powers to rule by decree and override democratically elected legislatures. If he thinks that the security of Soviet citizens is threatened, he can declare a state of emergency anywhere in the country without the consent of the local authorities. The only limitation is that the action subsequently must be endorsed by the working Soviet legislature, or Supreme Soviet, by a two-thirds majority.

Under article four of the law on states of emergency, the president has the right to take draconian measures to preserve public order. He can ban strikes, impose curfews, establish complete control over the media, cut telephone lines, control the movement of citizens, dismiss any state official, forbid demonstrations and suspend political parties.

The imposing array of powers available to Gorbachev does not appear to have intimidated Moldavian nationalists, who insist that they will not bow to his demands. Soviet television tonight reported disruption of a rally in the capital, Kishinev, that was designed as a show of support for the president's latest decree. Activists chanted "Down with the empire" and "Russians, go home."

To implement a crackdown on Moldavia or other republics, Gorbachev is likely to rely primarily on about 300,000 Interior Ministry troops and the KGB security police. According to some reports, several divisions of regular troops recently were transferred to the Interior Ministry, where they will report to Gen. Boris Gromov, the former commander of Soviet forces in Afghanistan.

To reassert his authority over nationalists, Gorbachev must make a tactical alliance with conservatives in the army and party. But if he moves too far in their direction, he risks compromising his own program and ultimately his position.

"I am afraid that an all-out confrontation between {the} center and republics might result in removal not just of the nationalist forces, but also a threat to Gorbachev himself. It might create a climate in which the moderates would be swept away by extremists," said Andrannik Migranyak, a political scientist who has been predicting the advent of a more authoritarian regime for the last year.

If Gorbachev succeeds in imposing his authority on the republics, the next target is likely to be the economy. At a conference in Moscow last month, leading Soviet industrialists called for a moratorium on strikes and a temporary halt in democratization. Kryuchkov suggested Saturday that there should soon be a monetary reform.

There is always a chance that Gorbachev will not follow through on his latest threats against Moldavia. Several presidential decrees on the disarming of vigilante groups and the vetoing of republican legislation have been quietly forgotten over the last year. According to Kryuchkov, there are about "400 armed formations" with a total membership of about 26,000 in the country.

Analysts, however, seem convinced that this time Gorbachev means business.