THE improving relationship between China and the Soviet Union has been strained over the self-assertive claims of Soviet republics bordering China. The Soviet republics have objected to concessions offered by Moscow in border talks with Beijing and demanded a say in determining their frontiers with China, diplomatic sources say.
The restive republics are unlikely to halt the steady rapprochement between China and the Soviet Union in trade, defense, Communist Party ties, and other fields since 1989, say the diplomats.
But the republics have upset the efforts by the two countries to quickly settle conflicting border claims that for centuries have symbolized the mistrust and enmity between them, they say.
The intrusion of the republics in the border negotiations is the most glaring sign of how the Kremlin has apparently resigned itself to the partial autonomy of regional officials in relations with China. Moscow Mayor Gavriil Popov flouted diplomatic protocol last October and visited Taiwan, the island ruled by the Nationalist rivals of Beijing's Communist leaders. Also, officials in the Soviet Union's Central Asian republics that border the far western Chinese province of Xinjiang are deepening their di plomatic contacts across the frontier, diplomats say.
Soviet officials resent the role of the republics in determining the Sino-Soviet border. But they must consider the republics' claims or risk inflaming the regional sentiments that threaten to rip the Soviet Union apart, the diplomats say.
``Now, if for instance Moscow gives a portion of a Central Asian republic to China, it will be like setting off a bomb in that republic,'' an East European diplomat says.
China and the Soviet Union skirmished over parts of the 4,500-mile-long border in the late 1960s. Beijing several years ago dropped a claim to vast areas of territory it says were taken from it by czarist Russia in unequal treaties in the 19th and 20th centuries. Still, thousands of square miles of land on the eastern and western parts of the border remain under dispute.
When Moscow and Beijing formally ended three decades of estrangement in 1989, the two countries swiftly agreed to solve the border problem. They privately pledged that negotiators from each country would yield on one stretch of the border in return for concessions on another part, say the diplomats.
THE quid pro quo collapsed last year when the Soviet Union's increasingly assertive republics objected to how Soviet diplomats were bargaining away their territory.
Opposition by the republics has drastically slowed the talks. Instead of trading concessions on different stretches of the border, Beijing and Moscow must take the more complicated and contentious approach of discussing each disputed section separately, the diplomats say.
Also, Soviet diplomats now consult with representatives from the border republics - Russia, Tadzhikistan, Kirgizia, and Kazakhstan - before making initiatives in the regular talks. The next round of negotiations is scheduled for April 11 in Beijing.
``Two years ago Beijing and Moscow thought they could smooth over their border disputes pretty quickly,'' says the East European diplomat, who spoke on condition of anonymity. ``But now that the republics have gotten in the way of the [border] negotiations, it will probably take many more years.''
The slowdown in border talks has apparently thwarted the desire of Communist Party General Secretary Jiang Zemin to conclude a visit to Moscow in mid-May by reaching a border agreement, the diplomats say. Mr. Jiang will be the highest ranking party official to visit Moscow since Mao Zedong went there in 1957.
Jiang betrayed his impatience with the pace of the talks on March 29. He said that Sino-Soviet relations since 1989 had made ``sound progress in all fields,'' but added that ``this does not mean that there is no problem between the two countries.
``For example, the Sino-Soviet boundary question has not yet been completely resolved,'' Jiang said, according to the New China News Agency.
Jiang and Soviet leader Mikhail Gorbachev are likely to sign a protocol that expresses the shared principles of the two countries on the dispute and identifies parts of the border that are no longer at issue, the East European diplomat says.
The Chinese delegation will also likely outline the limits it will tolerate in Soviet relations with Taiwan and seek assurances from Moscow that it will honor them, the diplomat adds.
Chinese diplomats have expressed deep concern to their Soviet counterparts over the growing trade and other contacts between Moscow and Taipei.
The two countries are also negotiating over the opening of a Soviet consulate in the Xinjiang regional capital of Urumqi, which would primarily be staffed by diplomats from the foreign offices of the Central Asian republics, says the East European diplomat.
Beijing has responded to the breakdown in central Soviet authority in several ways.
First, China has clamped down on the Turkic, Tibetan, and other restive minorities in its own empire, Chinese sources say. China's leaders relentlessly stamp out any secessionist sentiments that spill across the frontier.
Meanwhile, China is also promoting border trade in hopes of enlivening the economies of the comparatively backward regions that abut the Soviet Union.