China's relations with the Soviet Union have taken a long-delayed step forward with the visit of Soviet First Deputy Premier Ivan V. Arkhipov. During the first three days of his visit to China, which began Dec. 21, the two countries have agreed to set up a joint commission on economic and technical cooperation and to sign agreements on science and technology exchanges and trade.
The agreements are expected to be signed before Mr. Arkhipov returns to Moscow at the end of this week.
The top China hand among Soviet leaders, Arkhipov is on a clearly defined mission to improve trade and economic ties and thus to accelerate progress toward normalizing Sino-Soviet relations.
''We are convinced that there exists a large potential for the further expansion of mutually beneficial businesslike cooperation'' between the USSR and China, he said after stepping off the plane Friday.
His visit and the agreements it has brought will in effect reactivate government-to-government relations which have been dormant for more than two decades.
Before planning to head south today for Guangzhou (Canton), the Shumzhen special economic zone, and the industrial city of Wuhan, Arkhipov met three times with Vice-Premier Yao Yilin. He also met with Premier Zhao Ziyang Sunday.
The talks went smoothly, according to the Chinese Foreign Ministry. Besides trade and other economic matters, the two sides also exchanged views on international and other bilateral relations.
On the night of Arkhipov's arrival, Vice-Premier Yao said in a banquet speech that China's modernization would depend mainly on its own strength, an indirect reference to the years when China depended heavily on Soviet aid.
''To be frank, difficulties still remain in our relations. Differences between the two countries on how to normalize our relations have yet to be overcome. We hope that the two sides can finally make progress in this regard through common efforts,'' Yao said, according to the New China News Agency.
When Arkhipov was met at the airport Friday, Yao hugged him as an old friend. As the top Soviet adviser here during most of the 1950s, Arkhipov is a key link to those days when there were about 5,000 Soviet advisers in China and when Chinese children in Peking would greet any foreigners as ''elder brothers from the Soviet Union.'' Arkhipov also helped draft China's first five-year plan.
The China he is seeing is greatly changed from that of 1958 when he left. After he left, China began to reorient its Soviet-inspired, centrally planned economy to mesh with the Western-oriented, international trading system.
Recent reforms, for instance, have begun to decentralize foreign trade in a way that will make it increasingly difficult to coordinate an expanding barter trade with the Soviet Union. Some Chinese planners have projected Sino-Soviet trade will reach $5 or $6 billion by 1990, but Western diplomats say that a barter trade of this magnitude would be almost impossible to manage under China's new decentralized trading rules. The two-way trade is estimated to reach
Unlike 30 years ago when it was the main supplier of advanced technology to China, the Soviet Union is now a lagging competitor in China's search for partners in its modernization programs. Already China is exporting consumer goods to the Soviet Union in exchange for such products as heavy machinery and lumber.
When Arkhipov looks out over the high-rise buildings and industrial sites of the fast-paced Shumzhen special economic zone north of Hong Kong later this week , he will see a China moving quickly away from the orthodoxy of Soviet-style Marxism. On the day of his arrival in Peking, another front-page editorial appeared in the Communist Party newspaper, the People's Daily, elaborating on an editorial two weeks ago which criticized literal interpretations of Marxist theory.
The commentary, called ''More on Theory and Practice,'' emphasized that ''Marxism is not a dogma, but a guide to action.'' Marxist theory must be worked out in practice and should not be considered immutable, the article said.
''. . . Should we stick doggedly to some of Marx's assumptions made more than a hundred years ago . . . and accomplish nothing, or should we proceed from realities and push forward the Socialist cause in accordance with the principles and policies laid down by the Central Committee of the (Chinese Communist) Party? The answer is obvious.''
A longer commentary, appearing the same day, specifically defended the urban and industrial reforms outlined two months ago by the party. The reform decision ''made many breakthroughs in theory, and thus greatly enriched and developed . . . scientific socialism.''
Observers say that such articles suggest the leadership is waging a political struggle against those who oppose or at least have serious doubts about the sweeping economic reforms.