MOSCOW, NOV. 21 -- The head of a key faction in the Soviet legislature declared today that civil war has broken out across the country and said he will press for Mikhail Gorbachev's resignation if the Soviet president fails to assert his authority by next month.

Lt. Col. Viktor Alksnis, the 40-year-old chairman of the conservative Soyuz faction in the legislature, told the newspaper Sovyetskaya Rossiya that Gorbachev has allowed nationalists and liberal democrats to undermine the authority of the Communist Party and the central government and to begin breaking up the union itself.

"Under any other political system, leaders who fail to achieve practical change for the better -- to say nothing of their obvious failures -- are replaced. It's time that we, too, followed this universal rule," Alksnis told the newspaper in a lengthy front-page interview.

Sovyetskaya Rossiya, one of the country's most conservative papers, set off a national furor in 1988 when it published a neo-Stalinist manifesto by a Leningrad chemistry teacher that was supported by some of Gorbachev's conservative rivals. The Soviet leader's popularity is far lower now than it was then, and many politicians and analysts here contend that his ability to rule effectively has dwindled.

Gorbachev proposed last weekend that the Congress of People's Deputies, the country's supreme legislative authority, increase his executive powers when it meets Dec. 17. The Soviet president has won initial approval from the standing legislature, the Supreme Soviet, to eliminate the prime minister's job and give him direct control over government ministries. He also proposed that the Federation Council, the assembly of the leaders of the 15 republics, become his principal cabinet.

Many of Gorbachev's most persistent critics praised the move, although his main political rival, Russian President Boris Yeltsin, charged that Gorbachev merely intended to increase his own authority at the expense -- and without the consent -- of the republics.

At a news conference today, Yeltsin continued to criticize Gorbachev for failing to consult with leaders of the republics before making his proposals. Yeltsin said that perhaps the legislature should order a nationwide referendum on Gorbachev's bid for added authority. "If we want to know whether the people want a full presidency for Gorbachev or not, let's ask the people, conduct a referendum," Yeltsin said.

Alksnis made it clear that if Gorbachev did not begin to crack down on the various republics asserting their sovereignty, he would call for Gorbachev's resignation when the Congress meets. Alksnis told the paper that his comments did not represent the official line of the Soyuz faction but said the group would meet next week and discuss the issue. Soyuz claims the support of about 500 of the 2,250 deputies in the Congress of People's Deputies.

"If the president finally begins to fulfill his promises, that is, if he refuses to allow the collapse of the country and starts bringing things into order, then we will give him comprehensive support. If he once again limits himself to word games, we'll demand his resignation," Alksnis said. "This period is long enough to see if his words will be supported by deeds or everything will just stay as it is."

With old-guard figures such as Yegor Ligachev and former KGB chief Viktor Chebrikov now retired as a result of Gorbachev's maneuvering, Alksnis has emerged as one of the most prominent spokesmen of conservatives who fear the breakup of the union and the dwindling prestige and authority of the Communist Party, the military and the KGB secret police.

Although the overwhelming majority of Soviets are pleased about Gorbachev's achievements in foreign affairs and his campaign for political democratization, polls show that they have grown profoundly fearful about the precipitous decline in living standards in recent months and that they wonder if a firmer hand is needed.

In the Sovyetskaya Rossiya interview, Alksnis portrayed Gorbachev as a leader who acts only when it is too late. "His decrees remind me of a hurried man who gets to the train platform just in time to get the last train. Even those belated decrees are ignored, and no one takes responsibility," he said.

Alksnis said Gorbachev must declare "presidential rule" in the republics or risk losing his authority completely to "criminal" nationalists campaigning for independence and sovereignty in the Ukraine, the Baltic states and other Soviet republics. He also accused Interior Minister Vadim Bakatin and Alexander Yakovlev, Gorbachev's closest ally in the Soviet hierarchy, of allowing leaders of the republics to trample federal laws.

Asked about the conflicts in various areas of the Soviet Union, Alksnis said: "Real civil war has broken out in the country. In the majority of regions, it is true, it is still a kind of 'cold war,' but elsewhere it is already a matter of arms, with killings, people wounded and hundreds of thousands of refugees. If we don't stop the escalation of violence and mutual intolerance, large-scale hostilities could engulf the country."