WORLD REPORT EXTRA: The Coup and Beyond : National Agenda : There’s a New Sheriff--and His Name Is Boris Yeltsin : He saved Gorbachev--and the country. As payment, he’s demanding a weaker central government and a crackdown on the military, KGB and Communist Party.

MOSCOW —  President Mikhail S. Gorbachev was back in his Kremlin office on Thursday, and perestroika was saved from the rightist coup d’etat that had so shaken the Soviet Union--and the world--for three days.

But Gorbachev immediately faced a new challenge from the man who led the popular opposition to the putsch--Russian President Boris N. Yeltsin, who through his courageous resistance became the preeminent figure in Soviet politics.

With the collapse of the coup, the power balance in the Soviet Union shifted dramatically in Yeltsin’s favor, and he acted quickly to exploit the advantage in moves that would make him, not Gorbachev, the principal architect of the country’s future.

“An intense political struggle is coming, for now we are finally coming to the point of decisions about what sort of political system, what sort of economy we will have,” Andrei Kortunov, a leading political analyst, commented. “The putsch, in fact, brought things to the decision point. The stalling has to stop.”

Yeltsin, speaking at a victory rally on Thursday, called for the rewriting of the proposed Union Treaty to give even greater powers to the country’s constituent republics, of which the Russian Federation is the largest, and for a weaker central administration. Russia, he said, would have a new “national guard”--in effect the republic’s own army.

He called for a purge of those officials and military commanders who had supported the coup and for the reorganization of the government to end the concentration of power that enabled the plotters to mount their action. The vast powers of the KGB, the Soviet Interior Ministry and the military-industrial complex must be cut, he said.

And he demanded the seizure of the Communist Party’s property in punishment for its silence throughout the coup. Its newspapers, including Pravda, backed the self-proclaimed Committee for the State of Emergency and should be closed or reorganized under different editors, Yeltsin said.

“The reforms are still very much in danger,” Yeltsin said. “This putsch has shown that the structure of the (Soviet) Union is still very conservative . . . and we have got to reform the whole thing. We cannot postpone any longer the formation of a new structure.”

Yeltsin, typically blunt and fully aware of his new power, was laying down just the first of the conditions that Gorbachev will have to meet to win his continued support.

“The Union Treaty has got to be amended,” he declared, referring to the final draft that Gorbachev, he and other republic leaders were to sign last Tuesday. “This document must take into account the experience we have accumulated in the last three days.”

There will be further demands, however, as Yeltsin’s supporters made clear later in the day.

“We have earned the right to shape this government and to set its policies,” a Yeltsin adviser said. “We saved Gorbachev, we saved the reforms and, most probably, we saved the country from dictatorship and the civil war that would have followed . . . .

“Gorbachev should understand that people shouted for Gorbachev because Yeltsin told them to. These are the new political realities.”

As a new constitution is drafted over the next six months, as required by the proposed Union Treaty, Yeltsin will insist that the authority of both the central government and the national legislature, the Supreme Soviet, be sharply curtailed.

Party members will likely be removed from sensitive positions they hold in the government; using new authority from the Russian legislature, Yeltsin began purging coup supporters from regional governments on Thursday. Even with Yeltsin’s campaign against the party in the Russian government, party members still hold 80% of the posts there.

The transformation of the country’s centrally managed economy will be accelerated through the privatization of state-owned enterprises and the ending of collectivized agriculture.

And Yeltsin expects to nominate a number of key ministers in the central government, in effect establishing a ruling coalition with Gorbachev.

These demands could give the Soviet Union a much different shape in the future than that envisioned by Gorbachev.

The powerful Russia sought by Yeltsin could well bring the development of a looser confederation, binding the Slavic republics of Byelorussia and the Ukraine under Russian leadership in a union with the Muslim republics of Soviet Central Asia under the leadership of Kazakhstan’s president, Nurasultan Nazarbayev.

The strong federation sought by Gorbachev, which the central government would lead, seems far less likely than a week ago, and with that shift the whole political ground in the country moves--for each republic would be left free to work out its own reforms.

And as the old Russian tricolor of white, red and blue flew for the first time on Thursday from the Russian Parliament, it was Yeltsin’s vision, not Gorbachev’s, that appeared to have won the nation.

“Gorbachev will not get his way any longer,” Kortunov predicted. “Everything he wants, he will have to cast in terms that Yeltsin will accept, and what Yeltsin wants will become the focus of Gorbachev’s attention.”

Yeltsin’s demands, in effect, now form the country’s political agenda, and Gorbachev appeared at his press conference Thursday evening ready to comply.

He had not only been drained by the ordeal, but he seemed to sense that the president of the Soviet Union no longer commanded the scene as he did before the coup.

“I must say that (the republics) adopted a position of principle and, in particular, our Russian Parliament, our Russian deputies, our Russian government,” Gorbachev said. “And the leading role was played by the president of Russia, Boris Nikolayevich Yeltsin.”

Gorbachev’s own political agenda, in contrast to Yeltsin’s, is one of repair. “We have not returned to the status quo ante,” a Gorbachev aide said. “We have our president back, but the damage done was horrendous.”

He must reassert his authority, which was so diminished by the coup and by the weakness of his leadership that it exposed. He must rebuild his team of ministers and advisers after confessing that he had appointed to key posts men who had betrayed him. He must develop political and constitutional safeguards against further coups and purge the Communist Party of its hard-line conservatives.

Finally, Gorbachev must redraft his reform program, and there Yeltsin’s demands are likely to dominate, for the Russian president can claim a mandate--his own election in June, the popular support that thwarted the coup--that Gorbachev does not have himself.

But Gorbachev will likely not be faced with the same strong conservative opposition that has undercut many of his reforms over the past six years and forced him into countless compromises and retreats.

The failure of the rightist coup will likely discredit the democratic conservatives as well as those who tried to seize power.

The parliamentary group, Soyuz, tried but failed to take a position on the coup. The militantly Marxist groups within the Communist Party are likely to coalesce into one faction--and then go underground to avoid the coming purges.

And the party itself, already reduced to fewer than 15 million members in a nation of 290 million, will face a choice of either becoming an instrument of Gorbachev’s, and Yeltsin’s, reforms or finding itself pushed further and further from the center of power.

To the left, there will be intense competition to lay claim to the honor of having defeated the coup, but only Yeltsin’s Democratic Russia movement, its ally the Communists for Democracy and some of the independent labor unions stood up when it counted.

“With Yeltsin, the little parties have a role--otherwise they are insignificant,” the liberal editor of a leading newspaper commented. “After months and months of bickering and feuding and stalling, Yeltsin has suddenly become the only political vehicle for the left.”