THE DISTINCTIVE feature of the United States' current strategic situation is that the administration has allowed relations with the Soviet Union and China to deteriorate simultaneously. This is precisely a reversal of the theory and practice of American strategic policy in the 1970s. Then the effort was to use progress with the one communist power to bring about progress, or at least to brake retrogression, with the other. Now there is improvisation and drift.

Mr. Reagan has given top priority to testing the notion that the Soviet Union is an intrinsically hostile power whose impulse to expand must and can be deflected by the application of American will. The plain implication is that things will have to get worse, as Moscow reacts to the American challenge, before they can get better. Whether Mr. Reagan can stay this particular course is an increasingly interesting question, at home and internationally. That things are indeed worse with the Soviets is not in question at all.

This administration inherited a working China policy in which relations were moving forward by degrees, and the ever-explosive Taiwan question was being, at the least, carefully tended. Mr. Reagan's special partiality for Taiwan shook the ground. Former secretary of state Alexander Haig undertook a formidable steadying effort; it cost him dearly. Now things are off track again. A few weeks ago, Peking blamed Washington for raising "obstacles" and said it was necessary to ask whether the United States regarded China as a friend or an adversary -- the basic question, the very question, that Presidents Nixon, Ford and Carter had struggled to resolve. Dotting the "i," China has reopened general political talks with the Soviet Union after three years of deep freeze.

There is no telling where these talks may go. But a Soviet-Chinese reconciliation, or simply a return to bumpy but manageable relations on the state (not the party) level, has been a major concern for American planners since Richard Nixon went to Peking. Such a development would limit the United States in playing "the China card" against the Kremlin. It is not that responsible Americans have wanted to provoke Moscow and Peking to go at each other or to stay permanently strained. But there are advantages to the United States in having the two of them at odds and there would be disadvantages in having the two of them cooperating against this country. This is the zone of uncertainty Mr. Reagan is entering now.

The president may have his own calculus; it would be interesting to hear it. Others, however, can see his administration pushing toward a tighter clinch with Moscow on the central nuclear issues and stalling on the question of whether to make a fresh run at Peking. In both instances, the basic hurdle is the president's visceral, undifferentiated anti-communism. It keeps him from looking hard for what comforts there might be in improving relations separately with both the Soviet Union and China. It leaves him without a strategy to guide his policy.