President Reagan's remarks on nuclear weapons last week have prompted the Soviet Union to a new high-level statement of its own nuclear doctrine as well as handing the Kremlin a propaganda boon just as the steam was running out of the Soviet campaign against the deployment of new U.S. medium-range nuclear rockets in Western Europe.

Two themes emerged from Soviet criticism of Reagan's talk to a group of out-of-town editors in Washington last week.

First is President Leonid Brezhnev's unequivocal denial of Reagan's assertion that Soviet leaders believe a nuclear war is "possible" and "winnable."

"To count on victory in a nuclear war," Brezhnev said, "that is a dangerous madness."

Second is the Soviet focus on Reagan's speculations about the possibility of a limited nuclear exchange "without it bringing either one of the major powers to pushing the button" of all-out nuclear war. The Russians have cast this as a diabolical American plan to conduct a limited nuclear war in Europe and have gone out of their way to present it as such to Western Europeans.

Brezhnev's statement, ostensibly in response to a question by a Soviet correspondent, took on larger importance as an authoritative revision of Soviet nuclear doctrine. It clearly contradicted the statement of Moscow's military doctrine on nuclear weapons regarded until now by Western analysts as the most authoritative on the subject.

Marshal Nikolai Ogarkov, chief of staff of the Soviet armed forces and first deputy defense minister, outlined the Soviet nuclear strategy in an article on "military strategy" in the Soviet Military Encyclopedia, published in 1980.

"At the foundation of Soviet military strategy," Ogarkov wrote, "lies the proposition that the Soviet Union, based on the principles of its policy, will not employ these weapons first. It is also opposed in principle to the use of weapons of mass destruction.

"Soviet military strategy proceeds from the fact that if a nuclear war is foisted upon the Soviet Union, then the Soviet people and their armed forces must be ready for the most severe and prolonged trials. In this case the Soviet Union and the fraternal socialist states, in comparison with the imperialist states, will have definite advantages stemming from the just goals of the war and the advanced nature of their social and state systems. This creates objective possibilities for them to achieve victory. However, for the realization of these possibilities, the timely and many-sided preparation of the country and armed forces is necessary."

Breznev's statement, published in the most prominent spot in the Communist Party newspaper Pravda and by all other Soviet papers, said that "to try to defeat each other in the arms race and to count on victory in nuclear war -- that is dangerous madness." He added that "only he who has decided to commit suicide can start a nuclear war in the hope of emerging victorious."

In doctrinal terms, Brezhnev's statement amounts to the most authoritative affirmation of the concept of mutually assured destruction (MAD). It also reaffirmed implicitly the central Soviet argument that any use of nuclear weapons would escalate into a general nuclear war.

In terms of propaganda, the Soviet criticism of Reagan's statements asserted that it is the Americans -- and not the Russians -- who believe in fighting a nuclear war and emerging victorious. Soviet commentators continue to charge that the Reagan administration is preparing to wage a limited nuclear war in Europe. "Any use of nuclear weapons could have the gravest consequences," a Tass commentary said, "and all of mankind would be a loser."

Today, the Soviet press dismissed Reagan's explanation yesterday of his remarks to the editors last week. Quoting Reagan's clarification that "our strategy remains as it has been, one of flexible response," Tass called the statement a meaningless exercise in casuistry.

"It was designed to conceal the main thing, that is, that the United States, as before, not only considers a limited nuclear war possible but is also actively preparing for it," Tass said.

The main thrust of Soviet comments appeared directed at Western Europe and at encouraging antinuclear sentiments there. This is in line with Moscow's key objective of preventing the deployment of 572 medium-range nuclear missiles in Western Europe scheduled in 1983.