China and Japan are strongly demanding that the Soviet Union reduce the number of its SS-20 mobile missiles in Asia. The demand is an important part of the overall Chinese position in Sino-Soviet talks that begin here today. Leonid F. Ilyichov heads the Soviet delegation and Qian Qichen, the Chinese delegation. Both are deputy foreign ministers in their respective governments.
When Chinese Foreign Minister Wu Xueqian met with Japanese Foreign Minister Shintaro Abe in New York Sept. 29, the two ministers agreed that Soviet SS-20s in the Far East ''were extremely detrimental to the peace of Asia,'' according to Japanese sources. Mr. Wu told Mr. Abe on that occasion that the Chinese delegation to the Sino-Soviet talks would press strongly for a drastic reduction of these mobile nuclear-tipped weapons, according to the same sources.
Earlier, on Sept. 17, a commentary in the People's Daily demanded that the Soviet Union reduce the number of SS-20s it has deployed in Asia. The commentary was an answer to Soviet President Andropov's offer to destroy any SS-20s removed from Europe as a result of agreement with the Western allies, instead of deploying them to Asia.
China and Japan are both concerned about the presence of SS-20s in Asia. It is estimated that one-third of Moscow's approximately 350 SS-20s are presently deployed in Asia, the other two-thirds being targeted on Western Europe. In the past, Chinese and Japanese concern has focused on the possibility that if Moscow and the Western allies agree on reducing their respective intermediate-range nuclear missiles in the European theater, Moscow might transfer its missiles from Europe to Asia.
More recently, however, both countries have begun to argue that promising not to transfer SS-20s from Europe to Asia, as Mr. Andropov did, is not sufficient. There should be a substantial reduction of SS-20s in Asia, whatever the results of East-West negotiations regarding the European theater should be.
Thus, in a meeting here with North American journalists before taking off for the United Nations General Assembly, Foreign Minister Wu said, ''as for SS-20 deployment, we have always held the position that they should be drastically cut down and be destroyed on site. We hold the same position regarding the deployment of SS-20s no matter whether they are in the European part or in the Asian and Far Eastern part.''
The Japanese foreign office is known to hold a similar view. On this issue, therefore, Peking and Tokyo, while not allied, share a common concern, and the foreign ministers of the two countries have promised each other to keep in touch and to share information.
Whether this common concern will lead to East-West negotiations on intermediate-range nuclear missiles focusing on Asia is another matter. Neither China, Japan, nor the United States are keen on such talks with Moscow as of now.
Soviet sources contacted in Moscow last month say, however, that they are ready and that they would certainly bring up the question of Chinese intermediate-range missiles and American forward-based systems in Japan and South Korea. They estimate that China has 150 to 200 intermediate-range missiles.
Meanwhile, Sino-Soviet relations are expected to continue a gradual improvement, featuring more trade and cultural-sports exchanges, but without any major breakthrough. The Chinese are raising the SS-20 issue in the context of their three main demands: that Moscow withdraw its troops from Afghanistan, that it stop supporting the Vietnamese occupation of Kampuchea, and that it reduce its military forces targeted on China along the long Sino-Soviet border and in Mongolia.
Two previous rounds of Sino-Soviet consultations, in October last year and March this year, failed to show progress on any of these issues. Sino-Soviet trade, however, is growing, and reached $820 million in 1982. Cultural and sports exchanges have also been started, and Chinese readers are being told that the Soviet Union, like any other country, has its good points (no spitting in the streets, no pornography), and its bad points (drunkenness, vandalism, backward agriculture).
Before the Soviet foreign minister cancelled his visit to the United Nations General Assembly, Mr. Wu had been scheduled to meet him there. No new arrangements have been made so far for a Wu-Gromyko meeting, but Moscow seems anxious to have it take place.