THE QUIET news of the Soviet summer is that the drive for glasnost is deepening the drive for perestroika. Glasnost, or openness, gave the Soviet people the eyes, the voice, the courage with which to explore the political rot of the old Stalinism. Having seen it, they are using their expanded political liberty and confidence to construct an ever more direct attack on the pervasive economic rot. The process reveals an apt reversal of the traditional Marxist insistence that economics dictates politics; things are now proceeding in the opposite direction.

Whether the Soviet Union's fragile, lurching new politics can yet produce the economic initiatives and structures required for effective perestroika, or rebuilding, is far from certain. What is notable, however, is that many people in the Soviet Union are rejecting the widespread prognosis of their country's imminent and irreversible decline. They may be acting out of desperation and with little immediate prospect of success, but they are acting. That is the important fact underneath the ferment and the pessimism.

The source of this new activity can be traced to one man: Boris Yeltsin. This erstwhile prote'ge' of President Mikhail Gorbachev has emerged as his former mentor's tormentor-turned-incipient partner. Mr. Gorbachev had clearly come to a point where, despite his awesome achievements on the glasnost side, he lacked thrust and traction on the perestroika side. He was simply not radical enough -- he was too indebted to his Communist origins -- to recognize and exploit the forces that his own earlier reforms had set loose.

This is the contribution -- the tentative and potential contribution -- for Boris Yeltsin. He was bold and perceptive enough or, perhaps, opportunistic enough to catch the new wave of radical economic reform. It became one of the principal foundations on which he launched his own independent political career. He now has political control of the Russian Republic, the Soviet Union's largest and its economic heartland. The political struggle between him and Mr. Gorbachev has not been resolved, but Mr. Gorbachev has seen fit to accept Mr. Yeltsin as a legitimate source of an economic opposition and to use him as a kind of buffer against the old guard.

Mr. Gorbachev has even seemed to adopt the Yeltsin movement as a form of pressure on his own government, whose formal leader is Premier Nikolai Ryzhkov. Increasingly, the best and brightest of the original Gorbachev reform movements have moved to office and influence in the constituent republics, not least Boris Yeltsin's Russia. The central government's role in the economy has hardly passed, but it is changing under pressure all the time.

The other day, for instance, another benchmark of radical economic change was achieved. Interestingly, it came not from the Yeltsin camp but from the more cautious Gorbachev-Ryzhkov camp, which is increasingly playing catch-up. Premier Ryzhkov proposed that foreign businesses be allowed for the first time not simply to participate in joint ventures but to establish fully owned affiliates in the Soviet Union. There are a host of difficulties associated with this proposal, starting with the challenge of operating in the Soviet swamp and moving on to the riddle of how to take out salable products or hard currency. There will be no get-rich-quick breakthroughs for foreign businessmen.

The more salient point, however, is the evidence that boldness is growing in the bosom of the Soviet economic establishment. The Gorbachev model, which is widely identified with the worsening of economic conditions overall and especially with a cruel deterioration of consumer living standards, is more and more discredited and is being set aside. In its place is coming a new wave of reforms that are unequivocally designed on free market lines and that are sure to engage the Soviet Union more deeply in the global economy. The further the Kremlin goes down this road, the more difficult it is to go back.

Mr. Yeltsin recently declared that Soviet Premier Ryzhkov's government enjoyed no public confidence. No surprises there. But listen to what the premier said in response: "If Yeltsin turns out to be right, the government will have to resign." The West has a name for this startling process that Mr. Ryzhkov is referring to: accountability. There is a very long way to go in the Soviet Union but that is plainly the direction in which the imperatives of reform are moving the Soviet peoples. As the process becomes more serious and far reaching, it is bound to pose the United States its own challenge of how to engage productively with a movement that seems to be departing from the restructuring of socialism in the direction of democratic reform.