Soviet First Vice Premier Ivan Arkhipov left Peking today after trade talks that he said produced "positive" results.

But the two sides apparently did not address what the Chinese call the three major obstacles to improved ties with their former Communist ally: the Soviet occupation of Afghanistan, Soviet support for the Vietnamese occupation of Cambodia and the large numbers of Soviet troops stationed along China's northern border.

Western diplomats said a longstanding Soviet unwillingness to discuss these issues makes it unlikely that China's Foreign Minister Wu Xueqian will visit Moscow this May or June, as Soviet officialsoriginally had said he would. Last year the two sides agreed in principle to an exchange of foreign ministers' visits in 1986. Peking says no dates have been set for such a high-level exchange, which would be the first of its kind in more than two decades.

Responding to reporters' questions shortly before leaving Peking, Arkhipov said, "The talks were good, and the results of the negotiations were positive." The vice premier indicated, however, that he had not discussed with the Chinese possible exchange of visits by the two countries' foreign ministers.

Arkhipov, who visited China in December 1984, remains the highest ranking Soviet official to come here since 1969. But some observers noted that Arkhipov received a much cooler welcome on this visit than the earlier one. Moreover, throughout this visit, the Chinese press gave more play to the activities of three Cambodian leaders united in a coalition against the Soviet-supported Vietnamese occupation of Cambodia than it did to Arkhipov's activities.

He arrived in Peking a week ago for the first meeting of a new Sino-Soviet commission on economic, trade, scientific and technological cooperation. China's Vice Premier Li Peng, who was trained as an engineer in the Soviet Union, co-chaired the first round of talks with Arkhipov on March 16. A second round, on March 18, resulted in an agreement on further economic cooperation, according to the official New China News Agency. Details of this agreement were not disclosed.

The agency said that despite the progress made in the trade talks, Premier Zhao Ziyang, after meeting with Arkhipov on March 18, reported "no substantial progress . . . in political relations between the two countries in recent years.".

Today, officials from both sides signed a protocol having to do with the bilateral exchange of engineers and technicians.

In July 1985, China and the Soviet Union signed a $14 billion trade agreement for 1986-1990 under which Sino-Soviet trade is to double by 1990. The Soviet Union is currently China's sixth-largest trading partner, with the United States and Japan still far ahead in total trade volume.