''We hope that our relations with the United States will advance, not retrogress,'' Chinese Communist Party chief Hu Yaobang said during his recent visit to Japan.
In contrast to the honeymoon state of Sino-Japanese relations, Sino-American ties seem to have taken a sharp downward turn only a month before Premier Zhao Ziyang's planned visit to Washington in early January.
The immediate cause is Peking's anger over two actions of the US Congress referring to Taiwan as the ''Republic of China,'' and over President Reagan's use of the same term during his visit to Japan in November.
It seems hard to believe Peking would go so far as to cancel Mr. Zhao's planned visit and that of President Reagan to China next April over what may seem in Washington to be a fairly minor contretemps. But this is precisely what Mr. Hu, and Foreign Minister Wu Xueqian, who accompanied the Communist leader to Japan, are implying.
For behind what may seem like pique over language the US Congress or the President may have used is a more basic problem between Peking and Washington. Neither side has yet achieved a real sense of confidence and trust in the other's word.
Relations between countries are like those between individuals. Confidence and trust take time to establish, especially when the two sides have been estranged for as long as Peking and Washington were, and when in addition the US is a free enterprise, capitalist, pluralist democracy, while China is a socialist (i.e., communist) one-party state.
Moscow and Taiwan are the two poles around which Sino-American relations revolve. Mr. Reagan came to office as an avowed friend of Taiwan and a confrontational opponent of the Soviet Union. He seemed to be looking to Peking as a potential partner in his worldwide effort to contain Soviet expansionism while at the same time implying that he wanted to upgrade American relations with Taiwan, even to sell it more sophisticated arms.
Two years of difficult relations with Peking ended with the Aug. 17 communique last year in which Washington pledged not to sell sophisticated weaponry to Taiwan and to reduce arms sales year by year. Disputes
with Peking on other matters, such as textiles or tennis player Hu Na's request for political asylum, continued. But the atmosphere improved markedly last June when Washington announced it was relaxing restrictions on sales of certain high-technology items to China.
Defense Secretary Caspar Weinberger visited China in September. He was the third US Cabinet minister to walk on the Great Wall and tour the Forbidden City this year, the others being Secretary of State George Shultz and Commerce Secretary Malcolm Baldrige.
The joint announcement that Mr. Zhao would visit Washington in January 1984 and that Mr. Reagan would visit Peking in April the same year was made during Mr. Weinberger's sojourn. Subsequently Foreign Minister Wu went to Washington and was warmly received both by President Reagan and Mr. Shultz.
Yet somehow in Peking the impression prevails that Mr. Reagan would, if he could, have his cake and eat it, too. He wants a strategic partnership with Peking against the Soviets. But, as he said in Tokyo, he is not willing to abandon an old friend - that is, Taiwan. To Peking, this smacks of a perpetuation of the two-China policy Washington has formally abandoned.
This does not mean there is no flexibility in the Chinese position on Taiwan. Chinese officials point to the Aug. 17, 1982, communique on US arms sales to Taiwan as an example.
Foreign Minister Wu said recently that it was precisely because China takes Washington's historical ties with Taiwan into account that it has not insisted on an immediate cessation of US arms sales to the island.
''What else can you ask of us?'' Mr. Wu exclaimed to his interviewer. ''It's a very reasonable position.''
Peking officials say frequently that as long as Washington accepts a principle, the Chinese are prepared to be flexible on details. The principle is that Taiwan is part of China and that reunification of Taiwan with the mainland is an internal Chinese matter.
The flexibility comes in statements like the arms sales communique and Peking's various proposals to Taiwan aimed at peaceful reunification. Peking is upset over President Reagan's remarks and language used by the Senate because the references to Taiwan as the ''Republic of China'' seem to deny a principle that the Reagan administration and its predecessors formally accepted.
Meanwhile, in Washington there is irritation with Peking over the other pole of the Sino-American relationship - the Soviet Union. In private conversations, for instance with Mr. Weinberger, Chinese leaders have made quite clear their view that the principal threat to China's security comes from the Soviet Union. ''We know where the threat to our security comes from,'' Defense Minister Zhang Aiping told Mr. Weinberger.
But in public, China almost invariably cries a plague on both Washington and Moscow. This is a typical third-world attitude, but not one calculated to endear Peking to American congressmen.