The conventional wisdom of the past decade holds that when US-China relations improve, China-Soviet relations worsen. A related axiom states that when US-China relations improve enough, Moscow begins to show an interest in detente with Washington, lest it become too much the odd man out. (Sometimes this is stated: Kissinger to tea with Chou En-lai means Kissinger to dinner with Brezhnev.)
Neither formula seems to hold true today.
In fact, a case can be made that this great-power triangle works the other way round. Seweryn Bialer, the noted Soviet-affairs analyst and Director of Columbia University's Research Institute on International Change, argues precisely that case. He says worsened US-Soviet relations make improved Soviet-China relations not only possible but desirable to Peking and the Kremlin.
Precisely that appears to be happening, as Moscow has recently offered Peking a deal that would among other things create a Kremlin-Peking hot line similar to the one linking Moscow to the White House.
More substantively, the Soviet leaders have offered to remove nuclear weapons from the uneasy border between the two countries, to freeze the Soviet troop and weapons buildup along that border, to increase trade substantially, to help renovate the many Chinese factories built by Soviet crews in the 1950s, and to increase technical exchanges and resume cultural exchanges.
No one should leap to the conclusion that a deal is about to be consumated.
Both Peking and Moscow couple their offers with difficult demands. But Deng Xiaoping's China has moved steadily away from the period when it vehemently rebuffed all Soviet diplomatic and ideological approaches.
One of the most striking symbols of the changed relationship in the US-China-USSR triangle occurred during Secretary of Defense Caspar Weinberger's visit to Peking last month. Usually Chinese officials have warned visiting American officials about the Soviet menace. This time roles were reversed; Mr. Weinberger warned the Chinese.
Knowing that Mr. Reagan is staunchly anti-Soviet, Deng and company can ease their reflex reactions against Moscow. They can also criticize United States ''hegemonism'' alongside Soviet hegemonism, as they try to make the triangle more of an equilateral affair once more after two decades of distancing themselves from Moscow.
Several related motivations probably exist for the low-key but important shift in Peking.
First, there is the need for an umbrella over Deng's modernization program. When Moscow-Peking bellicosity was at its height, it may have appeared to the men in Peking that their best means of funding the modernization of China's economy (including its educational and technological base) was to keep defense expenditures under control and rely on closer ties with Washington to provide at least an implied umbrella against the USSR.
Now that the White House and Kremlin are engaged in renewed cold war, China's leaders doubtless feel their still infant modernization plans are best protected by a more balanced position between the two superpowers.
Second, and perhaps more important, Deng and his designated successors are trying to steer a tight course between (1) enough economic freedom to assure rapid modernization and (2) enough restraint on that freedom to assure party control.
They are also trying the difficult feat of decentralizing economic decisionmaking while still maintaining enough central control to avoid heavy deficit financing. (Big deficits are one facet of a modern Western economy Deng's planners do not want to import from Washington.)
In the past five years China's leaders have zigzagged between liberalization and reassertions of central control as they try to deal with this contradiction between modernization and the traditional party-knows-best attitude.
There can be little doubt as to which side China's bread is buttered on when it comes to technological aid, education, capital investment, and management know-how. The US (and Japan) are more essential than Moscow to China's rebirth in all these areas.
But with such aid comes the risk of rising individualism and loss of party discipline. Hence Peking's current tack in the direction of discipline.
And Moscow, driven by its classic worry about danger on both its European and Asian flanks, has sweetened its bargaining position in Peking. It's a push-pull equation. Moscow is pushed by Mr. Reagan and the Pershings; pulled by China's tack toward party orthodoxy.