President Brezhnev has played his ''China card.'' But the next move is still up to Moscow.
China has left little doubt that its ''real'' answer to Soviet overtures toward better relations awaits ''real'' good-faith actions by the Kremlin.
That is the implication of China's relatively mild, but firm, response to President Brezhnev's March 24 speech calling for improved relations. A senior Foreign Ministry spokesman in Peking declared, ''In Sino-Soviet relations and in international affairs, what we attach importance to are the actual deeds of the Soviet Union.''
In substance the Chinese response is in line with past statements. But its relatively moderate style underlined press reports from Peking that China would welcome a ''concrete'' Soviet gesture -- such as a freeze in deploying SS-20 missiles targeted on China from Siberia, a thinning out of Soviet troops on China's northern border, or even an acknowledgment of the need to tackle problems along the two countries' border.
The widely publicized Soviet bid seems calculated to appeal to Peking because of the strain in Sino-US relations over the Reagan administration's commitment to sell jet fighters to Taiwan.
But the Brezhnev speech is also a warning to Washington: If the United States continues its arms buildup against the Soviet Union, Moscow could retaliate by mending its fences with China. That would threaten NATO by freeing for use in Europe some of 45 Soviet divisions now deployed on China's border.
China has given no indication that it regards a token Soviet ''deed'' as likely. But it appears to be testing whether the US military buildup will change Moscow's intentions. If the Soviet Union feels a growing military threat, it might be tempted to move first toward a deal with China that would allow it to reinforce its East European front with some of the forces on China's border.
Last fall Moscow proposed reopening border talks, suspended in 1979 after the Soviet invasion of Afghanistan. But China has so far refused to respond on grounds there is no evidence of Soviet sincerity. Chinese sources have maintained a major improvement in relations requires reduction in Soviet forces on the Chinese border and reduction of the Soviet presence in Afghanistan and Indochina.
Despite deadlock on these issues, there are signs Chinese and Soviet negotiators are seeking common ground on improving trade and cultural contacts.
In his speech, Brezhnev said the Soviet Union is willing to agree ''without any preliminary conditions'' on new economic, scientific, and cultural ties as a step toward political reconciliation. China is making trade proposals to a Soviet trade mission now in Peking, and a Chinese mission visited the Soviet Union a few months ago. In these lower-level contacts each side will have ample opportunity to draw its own conclusions about just how sincere the other side is.