COLUMN ONE : Back to the Past--but How? : Coup leaders must now decide how ruthless they will be. The immediate objective is to forestall a popular uprising that could force them out.

Having seized power to save the Soviet Union from what they see as chaos and collapse, the country’s new conservative leaders must now show how ruthless they will be in using that power.

As Russian President Boris N. Yeltsin called for a nationwide strike in opposition to the putsch, and crowds of Muscovites surrounded the tanks deployed in the capital, the self-proclaimed State Committee on the Emergency Situation faced an immediate challenge on Monday.

After deposing Soviet President Mikhail S. Gorbachev, were they prepared to arrest Yeltsin, the country’s most popular politician? Were their soldiers ready to fire on crowds of demonstrators or striking workers? Would a show or even use of force intimidate a nation that has taken so ardently to democracy in recent years?

The issue was clear: The conservatives’ Kremlin coup had succeeded. But now they needed to consolidate the awesome power that they had seized and to forestall a popular uprising that could force them out.

Beyond that, however, there was the equally tough question of what strategy, what approach the conservatives want to implement with their new power.

Can the conservatives, who have increasingly undermined Gorbachev’s reforms, pull the country out of the crisis that they did so much to create? How would the government bureaucrats who mismanaged the Soviet economy for so long now save it? Can the country’s independence-minded republics suddenly be pulled back from freedom?

After lusting so openly to regain the untrammeled power they once exercised, can the Kremlin’s hard-line conservatives--the generals, the managers of the military-industrial complex, the KGB, the old-time party ideologists and apparatchiks --use it to reimpose orthodox Marxism-Lenininsm and bring back Soviet socialism?

On these questions will the ultimate issue be decided--will this coup succeed?

The very uncertainty of the answer increases the prospect for bloody confrontations in Moscow and other cities, perhaps even a civil war, as the Emergency Committee seeks to strengthen its power and troops poured into the Soviet capital.

With the Soviet defense minister, the interior minister and the head of the KGB security and intelligence service all members of the Emergency Committee, its readiness to use force is assumed.

Committee decrees, broadcast on Soviet state television on Monday, warned that active political opposition would not be tolerated, that the recently freed Soviet press would again be controlled by the state and that democratically elected governments in the country’s republics and cities would be deposed if they undercut the new policies.

Yet Gennady I. Yanayev, the acting Soviet president, was hesitant as he outlined the Emergency Committee’s policies at a Moscow press conference on Monday afternoon.

“I would like to do everything so that we don’t have to use force against the civilian population,” he said.

Yanayev and the other committee members appeared instead to place their hope that the nation will turn to them as political saviors from the mounting economic and social problems, giving them at least six months, the initial length of the state of emergency, to improve the life of the average Soviet citizen.

Already there was speculation that the government would empty its warehouses of emergency supplies of food and consumer goods to win popular favor through a burst of artificial plenitude.

Early decrees, moreover, ordered a freeze on consumer prices, cuts in the salaries of top officials and increased welfare payments for retirees and the poor.

Crash programs were announced for the construction of housing and in the distribution of food. The crackdown on crime is certain to be popular.

The new leaders also seemed to be counting on a large measure of apathy, of political fatigue and of irritation with liberal and radical “democrats” who had raised expectations that could never be satisfied.

Yanayev said the Emergency Committee would, in seeking retroactive approval for the coup, outline on Aug. 27 to the Supreme Soviet, the country’s legislature, further plans for reversing the nation’s economic collapse.

But for now, the political thrust of their emergency decrees appeared aimed at taking the country back to 1987--when perestroika, as Gorbachev’s reforms became known, was just beginning, when the central government was still in full control, when the economy was booming under the initial stimulus of change.

“We stand for a genuine democratic process, a consistent reform policy and the renewal of the people so that they can flourish socially and economically,” Yanayev said.

This seemed no more, however, than the typical retreat to half-measures that has come whenever the Soviet Union has approached the crunch issues in its reform efforts of the past four decades.

And the approach has failed repeatedly, for it has been founded on the belief that the Soviet system needs only “perfecting,” that it is fundamentally sound. Even Gorbachev had tried this initially before becoming convinced of the need for a total overhaul, starting with the country’s democratization and proceeding to a “full-blooded” free-market economy.

Yet, without a claim to constitutional legitimacy or even a mandate from the Communist Party, which has ruled since the 1917 Bolshevik Revolution, the Emergency Committee appeared hard-pressed on Monday to assert its authority--and power, with or without the use of force, became its priority.

“If the soldiers don’t fire . . . then this coup is gone,” commented Jerry Hough, a leading U.S. Kremlinologist at Duke University. “That’s where the crucial question lies.”

The immediate threat is not from Gorbachev, for he commands no troops, and, locked away for a “rest,” he cannot take his case to the people.

Instead, the challenge comes primarily from Yeltsin, whose Russian Federation is the country’s largest republic. And Yeltsin, who is as mercurial as he is charismatic, appeared ready on Monday to lead a nationwide resistance to the coup.

Viktor K. Grebenshikov, a reporter in The Times Moscow bureau, contributed to this story.