BEIJING — * In a clear sign that Beijing is concerned a breakup of the Soviet Union could spread unrest across its borders, China's vice president called yesterday for socialist unity in remote Xinjiang Province.Wang Zhen, who ended a nine-day inspection tour Saturday, urged the Army and people in northwest Xinjiang, bordering the Soviet Union, to rally around the Communist Party Central Committee and closely follow the socialist road, the official New China News Agency reported. In a veiled warning against unrest, he said China had successfully quelled antigovernment riots in 1989 in the Muslim-dominated region. China's state news media have reported the collapse of communism in the Soviet Union, but without comment. Diplomats said the Chinese Communist Party was not unduly alarmed that the demise of its Soviet counterpart would encourage popular revolt against its rule. Its main worry was that a Soviet breakup would spread instability along the long land border with China that is straddled by restive minorities. Xinjiang, four times the area of France, has a population of 15 million, about half of them Muslim. The region has been hit by periodic unrest, aggravated by ethnic turmoil in Soviet Central Asia. At least 22 people were killed when Chinese armed forces crushed a separatist uprising in the town of Baren near the fabled silk road city of Kashgar last year. Xinjiang officials have repeatedly condemned attempts to set up an independent state of East Turkestan.