It had to happen. A little glasnost, a little perestroika and the first thing you know the traders in Chicago are ready to set up a futures contract on the Soviet ruble.

And why not? Traders at the Chicago Mercantile Exchange figure that the political openness and economic reforms occurring in the Soviet Union could keep them in vodka and caviar for a long time.

The only roadblock to setting up futures trading on the ruble, and it is a major one, is that the government-controlled Soviet currency is not yet easily convertible into marks, pounds and dollars, according to the Merc's chief economist, Todd Petzel. While there is an official exchange rate of $1 for less than one ruble, the unofficial rate is about 20 to 25 rubles for $1, he said.

Although Soviet President Mikhail Gorbachev has indicated he would like to make the ruble convertible, it is not clear when that might happen, Petzel said.

But the Merc wants to be ready, and so it studying the idea and talking to the Soviets. The Merc already trades futures and options on six foreign currencies -- the German mark, the Japanese yen, the Swiss franc, the British pound and the Canadian and Australian dollars. Trading in rubles could eventually dwarf the volume of other European currencies, Petzel said.

Futures and options contracts allow investors to speculate on the future prices of currencies, baskets of stocks and commodities.