CHINESE President Yang Shangkun began a visit to Mongolia yesterday aimed in part at ensuring that China averts the separatism and anticommunism now dividing the Soviet Union.Mr. Yang is likely to emphasize his concern about growing Mongolian nationalism among China's ethnic minorities in the region of Inner Mongolia, diplomats say. Yang's comments - although his trip was scheduled long before the failed Soviet coup - would be the second sign since the start of the Soviet crisis that Beijing fears renewed instability among its minorities. "Beijing is definitely alarmed at the sudden devolution of power and anticommunism in the Soviet Union," says a Western diplomat in Beijing. "We'll probably be seeing in coming weeks other signs of its efforts to keep unrest outside its borders." During a nine-day tour of Xinjiang on the Soviet border, Vice President Wang Zhen urged citizens in the northwestern region to fully support the Communist Party, the New China News Agency reported Sunday. Mr. Wang made a veiled warning to Turkic nationalists in Xinjiang by recalling that Beijing last year crushed an uprising by Muslim separatists in the region. At least 22 people were killed during the rebellion. In Inner Mongolia, China recently arrested two Mongolian nationalists and put 26 others under house arrest, the human rights organization Asia Watch reported last month. China also shut down two small organizations made up of Mongolian intellectuals and Communist Party dissidents who advocated separatism for Inner Mongolia, according to a Chinese government document quoted by Asia Watch. Mongolia has emerged in the past several months as an inspiration for liberals and Mongolian nationalists in Inner Mongolia, the diplomats say. Last year Mongolia ended seven decades as a client state of Moscow. Its Communist Party agreed to share power with new democratic parties and held its first elections. Inspired by the severe setbacks for the Soviet Communist Party, thousands of Mongolians rallied in Ulan Bator during Yang's visit and called for the ouster of Mongolia's Communist Party, according to Western diplomats. Still, Yang has ample leverage for persuading Mongolia not to stir nationalist sentiments in Inner Mongolia, the diplomats say. Yang, the first high-level Chinese leader to visit Mongolia in 31 years, aims to offer vital assistance to a Mongolian economy that has suffered badly since Moscow withdrew numerous commercial benefits last year. China's president is scheduled to sign a loan package and several economic cooperation agreements, including one that will allow the landlocked country to ship goods through the northern Chinese coastal city of Tianjin. Beijing has already pressured Ulan Bator once this year into dropping plans that could have emboldened China's restive minorities. Mongolia canceled a visit by the Dalai Lama, Tibet's exiled leader, after China denounced the trip as a sign of tacit support for the Tibetan independence movement. A common heritage of Lamaist Buddhism has linked Mongolia and Tibet for centuries. China privately indicated that it would deny Mongolia access to Tianjin and other commercial benefits if the Dalai Lama's visit took place, the diplomats say.