The beefy soldiers who patrol both sides of the Sino-Soviet border are bracing for another frigid Siberian winter of watching each other watch the world's most heavily militarized boundary line.

Their lonely vigil along the icy, 4,500-mile frontier neatly symbolizes the frostbitten relations between their two communist capitals whose coziness in the 1950s set the capitalist West on edge.

Despite occasional feelers by both sides to resume border talks -- the most recent proposal was made by the Kremlin in September -- Sino-Soviet relations today remain badly snagged by memories of betrayal, competition for international influence and a common sense of danger dramatized by the standoff of more than a million Chinese and Soviet troops on the frontier.

Although Peking claims it is "studying" the latest Soviet overture, foreign and Chinese analysts give the proposal no more chance of untangling the 17-year-old dispute than Peking's last offer in June.

The day the June initiative was published by the Chinese Communist Party newspaper, the Soviet ambassador to China reportedly rushed to the Chinese Foreign Ministry to inquire whether the offer signaled Peking's readiness to drop certain demands that have stymied talks in the past.

"The ambassador got a flat 'nyet,' " a well-informed East European diplomat said.

Peking called off general normalization talks with Moscow after Soviet troops invaded Afghanistan in December 1979 and has warned that it will continue to snub the Kremlin as long as Moscow's 80,000 troops continue to occupy China's southwestern neighbor.

More specific border negotiations held separately from the broad normalization talks have been stalemated for years on the Chinese demand that both sides first withdraw their forces from the disputed areas -- a condition the Soviets reject because they hold most of the land in question.

"The main reasons why the talks have been postponed by the Chinese still exist," a European envoy said. "Nothing has changed to remove the obstacles. There's no ground for going back to the talks."

Recent months have seen the two communist giants move further from a border settlement by entering into arrangements with third parties that have frozen their positions and raised suspicions.

Moscow concluded a boundary treaty with Afghanistan in June, angering the Chinese, who claim the territory covered by the agreement was stolen from China by czarist Russia in the 19th century.

Moscow in turn cried foul after U.S. Secretary of State Alexander M. Haig Jr. visited Peking in June and unveiled plans to consider lethal arms sales to China that could strengthen greatly its border defenses.

An influential Chinese analyst views the latest Soviet overture as an effort to "drive a wedge between the Americans and Chinese" to head off the growing military relationship between the two Soviet adversaries.

"The Russians are trying to arouse suspicion in Washington of a rapprochement between China and Russia," said the analyst, who believes Peking will reject Moscow's offer. "It's just a trick."

Although the border clearly remains the flash point of Sino-Soviet relations, Peking seems far less preoccupied with the Soviet threat from the north today than in the 1960s, when Chinese citizens were exhorted to dig underground tunnels as a precaution against Soviet attack.

Xu Xin, deputy chief of the Defense Ministry's think tank, told members of the Trilateral Commission meeting in Peking last May that the Soviets would need 4 million to 5 million troops and 10 years to vanquish China.

"So we say the Soviet Union has a hard decision to make to attack China," he said in a speech that leaked out of the closed session.

Chinese officials throw a much wider net now, accusing Moscow not only of trying to encircle China -- there are Soviet troops in Afghanistan and along the common border as well as Vietnamese proxies on China's southern boundary -- but also of plotting to dominate the world.

Officials often seem to be reciting old cold war speeches of John Foster Dulles in describing the Soviet threat and the need to contain it. They even espouse a Chinese domino theory, warning that failure to "pin down" the Soviets in Afghanistan and the Vietnamese in Cambodia will just whet the polar bear's appetite for Thailand, Pakistan, Iran, the Persian Gulf states and the Strait of Malacca.

Visitors to China's military academy in Peking are treated to a graphic illustration of this theory. A huge wall map spread across an entire wall of the briefing room traces Russian expansionism from the 14th century reign of the Duchy of Muscovy, using flashing white lights to plot the history in chronological order.

In the Chinese calculus articulated by Xu Xin, world peace only can be preserved if the United States, Japan, Western Europe and the Third World join with China in a "tit-for-tat struggle on every front against Soviet hegemonism."

Claiming that it does its share by tying down a quarter of the Soviet Army on its northern border and most of the Soviet-backed Vietnamese regular troops on its southern end, Peking plays the role of the good shepherd trying to harden the anti-Soviet resolve of its would-be partners.

When the Reagan administration decided to resume negotiations with Moscow on the limitation of medium-range nuclear weapons in Western Europe, Chinese authorities warned of a Soviet ploy to "maintain and improve its superiority in Western Europe through talks."

Ever anxious to draw Japan into a greater security role in East Asia, Peking gives prominent media attention to Tokyo's estimate of the growing Soviet strength in the region and supports Prime Minister Zenko Suzuki's campaign to bring four Soviet-held islands back under Japanese control.

Former U.S. defense secretary Harold Brown, who visited China earlier this month, said top Chinese military and defense officials stressed their interest "in increased Japanese attention to security problems and their responsibility in the area."

"The Chinese view," Brown said in an interview, "is that the Japanese have 300,000 troops under arms. They can have 600,000 under arms and the Chinese said they wouldn't feel threatened."

China recently has redoubled its diplomatic efforts in the Third World, where it believes Moscow hopes to make important inroads so that it eventually can deny the rich natural resources of the developing nations -- particularly oil -- from Western Europe and Japan.

Despite China's stated hostility to the Soviet Union, foreign analysts believe the leadership includes advocates of a more even-handed policy toward the Soviets to reduce the security risk and the huge costs of maintaining a border defense.

Western diplomats believe there are Chinese officials who urge an improvement of state relations with Moscow to increase Peking's leverage in dealing with the United States on issues of vital concern, such as Washington's policy toward Taiwan.

They are seen as a small minority, however, with little influence among current leaders who prefer a strong commitment to an anti-Soviet coalition and a foreign policy free of wild lurches.

Although Moscow and Peking verbally slug it out in international forums and through their propaganda organs, the two antagonists maintain correct relations on a day-to-day basis. Every year officials from both sides meet for trade, river navigation and railroad transportation talks, and the participants always reach agreement.

Trade remains a relatively small portion of each side's overall foreign exchanges, although it is not insubstantial -- this year's trade agreement calls for $442 million. For imports of Soviet commercial aircraft, trucks and passenger vehicles, Peking exports metals and light industrial products.

National airlines make one flight a week to each other's capitals, and the trans-Siberian railroad travels from Moscow to Peking every seven days. However, there are no tourist or cultural exchanges.