Soviets Plan Exchanges to Buy and Sell Rubles : Moscow: Measure seen as a cautious first step toward convertibility of currency.

The Soviet Union today took an important step toward integrating its economy with the industrialized nations of the West, announcing that it will set up markets to buy and sell the ruble against other currencies.

The announcement, carried by Tass news agency, said the decision had been taken by the Soviet government Saturday as part of the introduction of a market economy. The exchanges are to open at the beginning of 1991.

The unexpected measure appeared to be a cautious first step toward convertibility of the ruble, an aim that even economists closely associated with the government have said is unlikely to be achieved before the mid-1990s at the earliest.

Under the decision, Tass said, a central exchange will be opened in Moscow and others in capitals of the 15 Soviet republics and major cities “for deals in foreign currency to be concluded at market exchange rates.”

The agency said Gosbank, the state bank, will control all operations at the new exchanges--which will be the first in the Soviet Union since the 1920s.

Gosbank, the Finance Ministry, the state Bank for Foreign Economic Relations and the republican ministries “will take measures to support the ruble’s rate against foreign currencies,” Tass added.

The ruble at present has two officially approved rates--an official one of 0.58 against the dollar and a tourist rate of 5.8 to the dollar. But on the black market, Soviet business publications say, the dollar is worth up to 25 rubles.

It had been widely assumed by foreign and Soviet specialists that the ruble could not be freely traded on world markets without devastating effects on the already crumbling economy before radical economic reforms took effect.

The government decision did not make clear exactly how far the ruble would be exposed.