China seems to be demanding an explicit commitment from Washington about the scaling-down of future arms sales to Taiwan.
This is how some observers here view China's frosty response to President Reagan's decision not to sell advanced fighter planes to Taiwan. Taiwan, in turn , was unhappy because it had not received the more advanced fighter planes.
The decision, announced in Washington Jan. 11, was conveyed to China by John Holdridge, assistant secretary of state for East Asian and Pacific affairs.
A Chinese Foreign Ministry spokesman said, ''The United States government has announced its decision to sell airplanes to Taiwan at a time when bilateral talks are going on. The Chinese government hereby lodges a strong protest against this.''
Washington appears to have expected a warmer response from Peking. A State Department spokesman indicated he had hoped the decision might contribute to better relations with China in the strategic field.
But the Chinese Foreign Ministry spokesman went on to say, ''The whole question of United States arms sales to Taiwan is a major issue affecting China's sovereignty which must be settled through discussion between the United States and Chinese governments. The Chinese government will never accept any unilateral decision made by the United States government.''
In short, while the US emphasized what it was not going to sell, Peking stressed the fact that, after all, the US will continue to sell planes to Taiwan. Peking zeroed in on this as a matter of China's sovereignty.
The longstanding American attitude has been that Washington cannot allow Peking to have veto power over what arms it will or will not sell to Taiwan. This was the single issue that kept Washington and Peking from normalizing diplomatic relations after President Nixon's epochmaking visit to China in February 1972.
Ultimately, in December 1978, the two sides decided to normalize relations while continuing to disagree on the arms sale issue, which arose because Peking refused to promise not to attempt to take Taiwan by force.
Taiwan is a part of China, and for China to renounce the use of force toward Taiwan is to renounce one of the attributes of sovereignty - so China insisted.
Now China is saying that arms sales to Taiwan by third parties also infringes China's sovereignty over the island.
Its most authoritative recent statement on the subject was a commentary in the People's Daily Dec. 31, which said, ''On the issue of how to solve the problem of United States arms sales to Taiwan, China both sticks to its principles and also is reasonable.''
The commentary then affirmed ''a fundamental principle,'' that ''the United States should properly respect China's sovereignty and should not interfere in its internal affairs and should not sell arms to Taiwan. Under the premise of recognizing this principle, both sides can hold consultations on ways to solve the problem.''
The language is ambiguous, and seems to suggest that China is not asking for an immediate cessation of American arms sales to Taiwan but for a commitment that over a period of time these sales will dwindle and cease. Foreign Minister Huang Hua is reported to have explicitly asked for such a commitment last year.
Yet, President Reagan feels that in deciding not to sell advanced fighter planes to Taiwan, he has gone as far as he can toward compromise with Peking without sacrificing what, for him and the US, is also a matter of principle: that the reunification of Taiwan with the mainland take place only by peaceful means and that US arms sales to Taiwan are the minimum required to guarantee this.
To make a commitment to Peking on future arms sales to Taiwan would not only infringe Mr. Reagan's campaign promises but would go far beyond what the previous Carter administration was willing to do. During a visit to China in August former President Carter explicitly denied making any agreement with China regarding such arms sales to achieve the 1978 normalization.
Among officials accompanying Mr. Holdridge on his visit to Peking are the deputy director of the State Department's political-military bureau and the director of the department's East European division as well. But as Mr. Holdridge continues his close-mouthed discussions in Peking, which are to last until Jan. 14, Sino-American relations seem so bogged down over Taiwan that it will be difficult to come to grips with larger global issues.
Sino-American relations have entered an extremely delicate stage; even the downgrading of diplomatic missions to charge d'affairs status cannot be ruled out.