The architect of the Soviet Union's new 500-day economic make-over warned American business yesterday against investing in his country without at the same time pressuring Moscow to move more decisively toward a genuine free-market system.

"I can tell you frankly I wouldn't put a cent of my own money" in the Soviet Union without change, he told a meeting here of the National Foreign Trade Council. "For helping now would just protract the agony of our old system."

With that statement, the blunt-spoken Stanislav Shatalin sounded more like President Bush or British Prime Minister Margaret Thatcher, who have both urged a caution in extending economic assistance to the Soviet Union, than Soviet President Mikhail Gorbachev, who has openly sought Western assistence. But Shatalin, a key adviser to Gorbachev, who describes himself as an economist and not a politician, tempered his comments with humor. He told of a Soviet proverb, used by Gorbachev during his visit here last June when he was seeking U.S. business investment, that "those who don't take risks don't drink champagne."

Although endorsing it in general, Gorbachev has had some problems with the details of Shatalin's plan now pending before the Supreme Soviet, particularly its provisions requiring a rapid dismantling of the system of central planning that has dominated the Soviet economy for 60 years.