President Reagan will have to tread cautiously and wisely to nurture along the still-fledgling relationship between the United States and the People's Republic of China. He no doubt values that relationship not only in its own terms but as a diplomatic asset on the larger chessboard of superpower politics -- that is, as a counterweight to Soviet expansionism. He will not extract the maximum benefit from that asset, however, unless he defuses present strains over the US sale of arms to Taiwan. Failure to do so would be an unfortunate setback for US diplomacy.
As in the past, both parties to the dispute may have to give ground to keep relations on course. It is in fact puzzling why Peking has been agitating the basic issue of arms sales to Taiwan. For some time it had focused primarily on the proposed US sale of the F-5G fighter which the Taiwanese wanted. Mindful of Peking's sensitivities -- and persuaded by the Pentagon that Taiwan did not really need the advanced plane -- the President decided not to let Taiwan have it. Still, the Chinese now seem to want an explicit US commitment to stop all arms sales to Taiwan.
This is, to be sure, an extremely emotional issue for the Chinese because it concerns territory and sovereignty. It is not altogether surprising that Peking remains mistrustful of the new US administration given Ronald Reagan's pro-Taiwanese stance during the election campaign. But China surely must understand that he can move only so fast in foreign policy given the pressures from his ultraconservative critics. Mr. Reagan has to take account of domestic politics no less than does Deng Xiaoping. In the American context, turning down Taiwan's request for the F-5G was not only a major concession to Peking; it entailed domestic political risk. The Chinese would therefore be short-sighted to hurt their own interest by such precipitate action as downgrading diplomatic relations.
The President, for his part, has not yet spelled out a clear-cut position with respect to the People's Republic of China, leaving it to his secretary of state and other aides to make policy on an ad hoc basis. This, combined with the long delay in arriving at a decision on the new Taiwan arms sales, is perhaps what has disturbed the Chinese, who may feel the US is still equivocating on the issue.
Thus it may be time for Mr. Reagan to be more forthcoming publicly about the US attitude toward the ''peaceful reunification'' of China and about his long-term intentions with respect to the transfer or arms to Taiwan. He certainly knows from Chinese actions in the past several months -- the anti-US rhetoric, the anti-Western actions at the UN, the courting of the third world -- that Peking is quite willing to put the Taiwan question above its own strategic and economic interests. So he must find a way of satisfying the Chinese even while preserving Taiwan's ability to defend itself.
In this connection the Taiwanese doubtless are also playing a brand of politics and trying to keep a hammerlock on Washington for purposes of their own counterpoint with Peking. The United States would never countenance a forcible takeover of Taiwan by China. It will continue to provide arms until such time as the two agree to be reunited. But the national interest would be disserved if the Taiwan military were allowed to undermine US ties with the People's Republic.
The Reagan administration, in short, has some thinking to do. What is US China policy over the long term? What are the limits of its relationship with Taiwan? When and under what conditions will arms sales end? These are the questions to be faced up if Washington is to preserve and enhance a relationship of immense importance to global stability.