MOSCOW, DEC. 14 -- Soviet President Mikhail Gorbachev turned up the pressure in his law-and-order campaign today, declaring void all decisions by governments of the republics and local regions that have disrupted supplies of food and other materials.

The decree, designed to strengthen the floundering central economy, is a clear rebuke to the republics that have struck trade deals with each other and with foreign countries without the Kremlin's approval.

Gorbachev also issued a presidential decree ordering state enterprises to honor their contracts through the first quarter of 1991 and not reduce their supplies. Countless enterprises have reneged on deliveries, especially to Moscow, citing political and economic grievances.

Gorbachev's decrees are part of his campaign in recent weeks to assure citizens, especially orthodox Marxists, that he intends to use his executive powers to reverse an economy plagued by chaos and the "war of laws" between Moscow and the republics.

Many officials and commentators here are convinced that Gorbachev has turned to authoritarian methods in recent weeks. They cite his efforts to strengthen his hold over the economy; his nomination of a hard-line former KGB official, Boris Pugo, as head of the Interior Ministry, which is responsible for domestic order; and his putting KGB chairman Vladimir Kryuchkov on television to issue a scathing denunciation of "anti-Communist" forces.

There have been times during the Gorbachev era when reformist forces have overreacted to Gorbachev's penchant for trying to steer a middle course, swerving between radical changes and periods of stabilization, but the radicals' mood has been especially gloomy lately.

Some analysts are convinced that Gorbachev is reacting to pressure from within the Communist Party, the army and KGB to strengthen his hold on power, insist on order and cease compromising with nationalist movements in the Baltic states and elsewhere.

In the latest issue of the liberal weekly Moscow News, a number of prominent analysts and deputies write that next week's session of the full legislature, the Congress of People's Deputies, will show Gorbachev trying to reassert authority.

"I think we are even seeing a creeping militarized coup. Not military, but militarized," said one of the commentators, Yuri Levada.

Gorbachev is likely to hear even more criticism at the Congress from conservatives in the Soyuz faction and in other groups. Leaders of Soyuz, which has a membership of about 500 of the 2,250 deputies, have said they could demand Gorbachev's resignation.