Frustrated by strained relations with the United States and fearful of plans for a massive new punch in NATO'S arsenal, Soviet President Leonid Brezhnev virtually ignored the New World in favor of the Old tonight in his major foreign policy address from East Berlin.

By announcing unilateral withdrawal of up to 20,000 Soviet troops and 1,000 tanks from East Germany in the next 12 months, Brezhnev shrewdly and dramatically sought to reinforce Kremlin attempts to show itself as a reasonable neighbor interested in reducing European tensions.

Coming after a gathering here this week of European Socialist leaders, and two months before a NATO council meeting that may decide on new medium -range missiles for the Western alliance, Brezhnev's announcement is sure to have wide impact on the continent.

He underscored this Kremlin calculation by casting the proposed basing of Pershing II missiles almost solely in terms of a U.S. scheme concocted with West German assistance. While addressing himself directly to the West Germans, Brezhnev had only scant words for the United States and they were mostly unpleasant.

"The actions of our partners go too often in a different direction, Brezhhev complained. The supporters of the arms race use any pretexts to heat up the situation and whip up military preparations."

Although the Soviets have said repeatedly that ratification of the second strategic arms limitation treaty by the U.S. Senate is a cornerstone of detente, Brezhnev had only scant words on this issue and nothing at all to say about the Cuban troop controversy which has rolled U.S. domestic politics and stalled the ratification process.

Seen from here, there was little reason for the Soviets to raise the Cuban matter, since in their view President Carter's own countermoves have not forced any concessions from the Soviets. In fact, they have raised Western European concerns about Washington.

By avoiding larger issues of East-West relations, Brezhnev followed the instincts that have governed him during his 15 years in power. He has focused chiefly on matters at hand and kept clear of adventuresome initiatives.

With this speech, he made clear that the issue of new medium-range missiles for NATO -- while raising the threat of improved military strength for the West -- also holds out the possibility of a new dialogue among the Europeans. The Kremlin has had some success in the past by focusing heavily on a single arms issue. The best recent example was the intense propaganda campaign directed against U.S. plans to reequip its West European forces with an enhanced radiation, or "neutron bomb" warhead for artillery and tactical rockets.