Peking — Within hours of Secretary of State George Shultz's departure from Peking, the official Xinhua News Agency published a commentary that revives all the sourness in Sino-American relations that Mr. Shultz's visit was designed to assuage.
Taiwan remains the chief obstacle in the way of improved relations between Washington and Peking, ''and especially United States arms sales to Taiwan,'' the commentary said.
''Unless this problem is resolved,'' the commentary said, ''mutual trust between China and the United States is out of the question . . . .'' This, the commentary said, is what Shultz's interlocuters, who included Premier Zhao Ziyang and advisory council chairman Deng Xiaoping, told the secretary of state.
Earlier, American delegation sources had said that Taiwan occupied only one-half hour out of eight hours of talks Shultz had had with his Chinese counterpart, Wu Xueqian. This half hour, it now appears, must have consisted largely of a recitation of Chinese complaints, including charges that the United States had not lived up to the provisions of a joint communique signed last August.
The most serious complaint, the commentary stated, was that ''the ceiling set by the US for its arms sales to Taiwan exceeded the maximum annual figures'' published by the US government. No figures were given.
Shultz told the Chinese, according to an official traveling with his delegation, that the US intended to observe the commitments made in the joint communique, the principal one being that arms sales to Taiwan would steadily decrease.
Chinese leaders told Shultz, according to the commentary, that the US-Taiwan Relations Act, which authorizes arms sales to Taiwan, ''is a serious stumbling block in the way of Sino-US relations.''
The commentary said nothing about a Shultz meeting with the Chinese defense minister, Zhang Aiping, a meeting that was arranged after Shultz arrived in Peking and that was taken by US delegation sources as a sign of Chinese warmth toward the Shultz mission. Nor did it say anything about the White House announcement that Premier Zhao Ziyang had accepted President Reagan's invitation to visit Washington ''in 1983.'' Chinese sources, while confirming Mr. Zhao's acceptance of the invitation, have consistently refused to pin down a specific time.