HAVANA -- The Soviet Union, while continuing to meet Cuba's critical demand for oil, has sharply reduced its overall trade subsidy and is withdrawing up to 2,000 technicians -- two-thirds the total of a year ago -- according to Soviet and Western diplomats.

Soviet Ambassador Yuri Petrov said 1,000 Soviet technicians have left Cuba in the last year and indicated that nearly as many may depart in the near future. The drawdown, set in motion shortly after Soviet President Mikhail Gorbachev's visit to Cuba two years ago, would leave about 1,000 Soviet technicians in Cuba, the lowest number in years.

"We don't see any tragedy in this," said Petrov in a news conference with foreign journalists Jan. 18. "We think it's the right policy that we've . . . maintained now into its third straight year."

Petrov sought to play down the reduced assistance, saying the technicians were leaving as projects were being completed, and that Cuban technicians were capable of taking their places. He said remaining technicians would be assigned to strategic projects, such as building a nuclear power plant scheduled to be completed by 1993 at Cienfuegos, southeast of Havana.

But other diplomats in Havana said the Soviet withdrawal appears to have accelerated as Cuba is facing one of its most difficult economic situations in the 32 years of rule by President Fidel Castro. And, they said, the Soviets have begun to demand that the remaining specialists be paid in dollars, which are in critically short supply in Cuba.

Moscow's shifting stance toward Cuba, which has already forced the Castro government to take profound austerity measures, is due less to Soviet disenchantment with its longtime Communist ally than to severe Soviet economic problems, diplomats said.

W. Raymond Duncan, a former CIA analyst who has written about Soviet-Cuban relations and who recently visited Moscow, said: "They don't want to abandon an old ally, but they are definitely trying to ease off of that tight relationship. The basic relationship is going through a fundamental change."

Nonetheless, there is a sense here that Cuban officials are rooting hard for a return to authoritarianism in the Soviet Union, a development that presumably would mean a resurgence of hard-liners in Moscow who are more sympathetic to Castro and more likely to shore up dwindling Soviet aid to Havana. "When {former Soviet foreign minister Eduard} Shevardnadze gave his resignation speech warning about a dictatorship, you could practically hear the hoorays around here," said one envoy.

The Soviets have reduced their presence in Cuba substantially in the Gorbachev era. Duncan said the Soviets had about 7,000 civilian technicians in Cuba in 1985.

Duncan, now a professor at the State University of New York at Brockport, said that in 1985 the Soviets also had a 2,800-man combat brigade and another 2,800 military advisers stationed on the island. In addition, he said, some 2,100 Soviet technicians were stationed at the Lourdes electronic intelligence facility outside Havana, one of the main Soviet listening posts abroad.

U.S. and European analysts have estimated that more than 2,000 Soviet military advisers are in Cuba now, a figure that Petrov declined to discuss. "There will be as many as necessary . . . for a normal life," he said, repeating the longstanding Soviet position that the United States' continuing hostility toward Cuba prevents a complete withdrawal of the Soviet military presence.

Trade with the Soviet Union, which accounts for about 70 percent of Cuba's international commerce, also is shifting significantly. Soviet and Cuban officials signed an accord in Moscow Dec. 29, setting general levels of trade for 1991 but leaving to negotiators the sticky task of determining important details, including some prices.

While previous bilateral trade pacts have covered five-year periods, the accord signed last month extends only to the end of this year -- a reflection, diplomats say, of the economic uncertainty in the Soviet Union.

The pact assures Cuba of receiving 70 million barrels of petroleum this year, the same amount it received last year and the level that most analysts consider necessary to avoid outright economic disaster. Cuba, which is heavily dependent on petroleum for its energy needs, receives about 90 percent of its oil from the Soviets.

"The most important thing about the agreement is stability," Carlos Aldana, ideology chief of the Communist Party's Central Committee, said in an interview with the Spanish magazine Cambio 16. "We have passed from uncertainty to certainty -- now we know what we can count on."

In return, Cuba agreed to supply the Soviet Union with 4 million tons of sugar, plus nickel, citrus, medical supplies and other products.

The pact envisions a more favorable trade ratio for the Soviets. In exchange for a ton of Cuban sugar, the Soviets used to send about 27 barrels of oil, but this year agreed to ship only about 18 barrels.

But the key element in the deal was an agreement to assign world market prices, calculated in dollars, to the commodities covered by the pact. Cuban-Soviet trade previously was a sweetheart deal for Cuba -- a barter arrangement based on rubles, which are not convertible into hard currency.

Both sides have kept the new prices secret, or hinted that they remain to be set. But diplomats familiar with the accord said the shift toward world prices favors the Soviets, who have been paying far higher prices for Cuban sugar.

Petrov said the Soviets would charge Cuba the world price for oil, now about $24 a barrel. But he added, "We cannot exclude the possibility that due to recent events in the Persian Gulf, we will have to revise . . . these prices."

Cuba, which has hard currency reserves of only about $65 million, would be hard-pressed to absorb any increase in petroleum prices. If they were to rise, the Soviets would face the choice of cutting oil deliveries, thus crippling the Cuban economy, or allowing Cuba to run up its already massive bilateral debt -- something that Moscow is loath to do.

Castro, keenly aware of the looming danger of the gulf war and higher oil prices to his and other Third World economies, has warned Cubans to expect the worst.