The Soviet Union launched a major new propaganda drive today to counter the impact of President Reagan's arms control proposals by portraying them as an attempt to "deceive" public opinion and undermine President Leonid Brezhnev's forthcoming visit to Bonn.

Initial Western reaction to Reagan's speech yesterday appears to have prompted concern here that Moscow could lose propaganda momentum in encouraging West European opposition to the stationing of new American medium-range nuclear missiles.

A rash of commentaries today appeared designed to maintain that momentum by renewed exploitation of Reagan's recent remarks that "an exchange of tactical nuclear weapons" in Europe was conceivable without escalating into an all-out exchange between the United States and the Soviet Union.

The Soviets have been using the president's casual statement to stimulate nervousness and doubts in Western Europe about Reagan's nuclear policies.

The government newspaper Izvestia tonight set the central theme of Soviet commentaries by asserting that yesterday's speech was designed to "impress on uninformed persons" the notion that the Reagan administration has developed a peace initiative of its own.

The official news agency Tass said Reagan's central purpose was to "cast aspersion in advance on the sincerity of statements" Brezhnev will make on his visit to West Germany that begins Sunday.

Reagan's objective, Izvestia concluded, was to create "a propaganda cushion" to absorb "adverse political consequences" of his policies. It identified them as the pursuit of "a fresh round in the nuclear missile race, deploying new U.S. missiles in Europe and preparing a limited nuclear war on the continent."

The Izvestia commentary was written by Sergei Losov, the general director of Tass.

By coincidence, however, the Soviets were engaged in some missile rattling of their own today. Reagan's speech came on the eve of the official holiday honoring Soviet missile forces and today's press was filled with articles about a "qualitatively new level of development" they have reached.

The deputy commander of Soviet strategic forces, Gen. Yuri Yashin, said in an article that his rockets "are capable of quickly and successfully dispatching to a target a colossal power to deal unavoidable blows to the aggressor, wherever he might be."

A commentary by the deputy chief of Tass, Anatoly Krasikov, asserted that the Soviet government was ready to "go as far as the West will be prepared to go" toward "lowering the level of military confrontation in Europe and in the world."

But, he continued, the Americans are determined to gain military superiority under the "cover" of responding to "a mythical Soviet military threat." He said the deployment of 572 Pershing II and cruise missiles would give the West 50 percent superiority--"let alone the qualitative leap"--over the Soviet Bloc.

The American policies, he continued, were particularly "sinister" because of "Reagan's refusal to exclude the possibility of a first, or warning, nuclear strike on the Soviet Union" and his "frank discussions" about a possible limited nuclear war.

As a result, the commentator charged, Reagan has created "not a mythical but a real threat to life in Europe and throughout the world. The power which proclaims itself the defender of Western values calls into question the very existence of civilization."

Krasikov concluded by asserting that Moscow does not intend to drive a wedge between the United States and its NATO allies and that it is prepared to cooperate with each NATO member separately or "with the entire capitalist world as a whole." He added, "To cooperate, however, one must, first of all, be alive."

A good part of the Soviet dispatches is devoted to assessments of the East-West balance, with figures advanced here showing the East slightly behind in most areas, including the number of soldiers on active duty as well as the numbers of those deployed in Central Europe.

While dismissing figures advanced by Reagan yesterday as "mysterious" and "fantastic," the Soviets have gone out of their way to maintain a tone of reasonableness and moderation. This suggests how sensitive the Kremlin has become on the issue of the new American missiles.

The visit to Bonn by Brezhnev, who will be 75 next month, in itself demonstrates the importance Moscow attaches to West Germany. There has been speculation here that Brezhnev would use his Bonn visit to announce some significant Soviet concessions in an effort to strengthen antiwar movement in West Germany and the rest of Western Europe.

So far, there has been no substantive discussion of the problem of reduction of medium-range nuclear weapons in Europe. Privately, the Soviets said Reagan's proposal on this issue could not conceivably be taken seriously. Brezhnev had publicly asserted that no leader in his right mind would consider removal of all SS20 missiles in exchange for the decision to abandon the deployment of the new American weapons.

In his speech, Reagan had demanded "dismantling of" not only SS20s but also SS4 and SS5 missiles.

But diplomats here said both sides are making exaggerated claims and demands to win the preliminary round fought in the public arena before serious talks get underway.