Soviet President Leonid Brezhnev tonight said the Soviet Union would unilaterally withdraw up to 20,000 of its troops and 1,000 tanks from East Germany during the next 12 months.

The Kremlin chief also offered to reduce the number of nuclear medium-range rockets in the Soviet arsenal aimed at Western Europe if the North Atlantic Alliance refrains from any new deployment of similar U.S. rockets in Western Europe.

The Soviet leader coupled his conciliatory statements with a blunt warning to Western European countries that their acceptance of such U.S. rockets would "radically" change the balance of power and prompt the Soviet bloc to take "additional steps" to beef up its military.

In a major speech here on security policy -- which was carried live in Moscow -- Brezhnev made no direct reference to Soviet-American tensions created by the presence of a Soviet brigade in Cuba.

But the tone of his speech and its conciliatory gestures appeared designed to create a better atmosphere for East-West detente.

Speaking at ceremonies marking the 30th anniversary of the founding East Germany, the Soviet leader urged continued East-West efforts to curb the arms race. His speech was mainly directed at West Europeans, and he singled out West Germany for his strongest direct warning against accepting U.S. medium-range missiles.

Brezhnev, 72, pledged that the Soviets will "never use nuclear weapons against those states which refuce to produce or acquire such weapons for themselves and do not have them on their territory."

"We must say bluntly," he added, "that the implementation of these [western] rocket projects would radically alter the strategic situation on the European continent, poison the international atmosphere, and naturally we would have to take necessary, additional steps" to strengthen our own security.

"If the Federal Republic of Germany [Est Germany] took these new rockets it is not difficult to imagine what consequences would await her if this weaponry were ever put to use."

After singling out West Germany, Brezhnev said the other West European allies also would have to consider the consequences.

In an oblique reference to President Carter's speech Monday on the Cuban issue, Brezhnev said that Western statesmen "to judge by their words, want" peace. He added however, that "too often the deeds of our partners go in another direction."

The Soviet leader's generally, conciliatory tone seemed designed to help save the pending SALT II treaty in the U.S. Senate and to relieve pressure built up on the issue of Soviet forces in Cuba.

The question of whether the NATO allies will take steps to modernize their aging tactical nuclear weapons in Europe in an effort to balance new medium-range Soviet rockets already in place is one of the most crucial arms questions of the decade. The Kremlin appeared to be making an all-out verbal effort to stop the West from acting.

Ministers from NATO countries already have indicated that the alliance will approve formally the deployment of new U.S.-BUILT Pershing missiles and cruise missiles at a NATO meeting in December. Both missiles would give NATO capability, for the first time, to reach targets in the western Soviet Union from launches in Western Europe.

This approval would then have to be followed by parliamentary approval in several countries where these controversial missiles are likely to be based, including West Germany, Belgium, Holland, and Britian.

That approval is still far from certain. Brezhnev's conciliatory gestures and verbal offensive undoubtedly are an effort to influence those deliberations as well as the December NATO meeting and a crucial meeting of the ruling Social Democratic party in West Germany also scheduled for early December.

Brezhnev called his pledges of troop cuts and his offers to negotiate a new concrete demonstration of the love of peace and the good will of the Soviet Union and its allies.We call on the governments of the NATO countries to give due evaluation to the initiatives of the socialist states and follow our example."

[In Washington, the State Department called Brezhnev's offer of troop reductions "positive," AP reported.]

Brezhnev, his words occasionally slurred during a 35-minute speech to 3,800 invited guests in East Berlin's showplace parliament building, directly attacked the widely accepted Western view of a major Soviet arms buildup during the last several years.

Referring to the stalled six-year-old East-West talks on mutual force reductions in Central Europe, Brezhnev said his plan "to cut back unilaterally the number of Soviet troops in Central Europe" represented "an example of moving from words to real actions."

He added: "In the course of the next 12 months, up to 20,000 Soviet servicemen, 1,000 tanks and a certain quantity of other military technology will be withdrawn from the territory of the [East] German Democratic Republic."

As chairman of the Soviet defense committee, I declare firmly that over the past 10 years the number of delivery vehicles for medium-range weapons on the territory of the European part of the Soviet Union has not been increased by one rocket or one aircraft.

"On the contrary, the number of medium-range rocket launchers as well as the power of these rocket nuclear warheads has been somewhat diminished. The number of medium-range bombers has also been cut back."

"Meanwhile," he stressed, the Soviet Union does not deploy such weaponry on the territory of other states at all. Over a number of years, we have not increased numerically our forces based in Central Europe."

Furthermore, he said, "we are ready to reduce, in comparison with the current level, the number of medium-range nuclear weapons based in the western regions of the Soviet Union, but of course only if there is no additional deployment of medium-range nuclear weaponry in Western Europe.

The Kremlin, he siad, was prepared to put medium-range nuclear missiles on the agenda of the next phase of Soviet-American strategic arms limitation talks, SALT III.

"In the framework of these talks we agree to discuss the limitation not only of intercontinental but also of other types of weapons, although naturally taking into consideration all the relevant factors and observing strictly the principle of equal security of the sides," he said.

Brezhnev's unilateral pledge to reduce Soviet troop strength in East Germany affects the largest concentration of Soviet power outside Soviet boarders.

The Soviets, according to Western estimates, have about 22 divisions in East Germany totaling 400,000 soldiers and airmen. They also have more than 7,000 tanks. For the Soviets, this is the front line just as West Germany is for NATO.

The Soviet chief also offered to negotiate lower troop limits on European military maneuver agreements, which were first developed as confidence-building measures during the 35-nation European Security Conference in Helsinki in 1975.

The question of whether to deploy the new U.S. atomic weapons in Western Europe is very similar to the one the Carter administration faced last year on deployment of the so-called neutron bomb.

At that time, Carter said he would withhold a decision and await Soviet moves on arms control. The Soviets, however, have continued to deploy the SS20 multiple warhead medium-range rocket of which more than 100 are already in the field, Western sources say.

The situation has created a severe problem for West Europeans who are concerned about the Soviet strategic edge in Central Europe, yet do not want to alienate the Soviets.

The new NATO weapons question is likely to be linked by West Europeans with proposals for arms control. Today, Egon Bahr, a leading figure in West Germany's Social Democratic party who had been sharply critical of U.S. plans to produce neutron bombs, called on the Soviets to stop production of the SS20 as a preliminary step to future SALT III negotiations.

The heads of all Warsaw Pact governments, except maverick Romania, were on hand to help the East Germans celebrate. Others on hand included PLO chief Yasser Arafat and Vietnamese Defense Misinter Vo Nguyen Giap.