For the first time in at least five years, Peking has sent an official anniversary greeting to Communist rebels in Thailand, signalling another step in China's increasingly energetic, if sometimes puzzling, diplomacy in Southern Asia.

The message from the Chinese Communist Party praising its Thai counterpart on its 35th anniversary for "encircling the cities as Peking government in Bangkok that is the Thai Communists' sworn enemy.

In the last few weeks the Chinese have appeared to welcome the recently reshuffled Thai cabinet and perhaps have encouraged neighbouring Communist states to improve relations with the latest crop of Thai admirals and generals.

In the last two months Chinese Communist Party Chairman Hua Kuo feng has entertained both the Cambodian leader, Pol Pot, apparently a friend of China, and the Vietnamese party leader Le Duan, whose ties to Moscow make him very suspect in Peking. Hua has apparently served as a go between in reducing border clashes between Cambodia and Thailand, whose former Premier, Kukrit Pramoj, was also a recent visitor to Peking.

On balance, the Chinese in the wake of the U.S. withdrawal from Indochina and the political decline of the most radical elements in Peking have become a force for stability in the region, if only for the time being and for their own special reasons.

The visit this week by Ne WIn, president of reclusive Burma, to the even more reclusive Cambodia was likely expedited by China one of the few friends either of these xenophobic states has in the world. Some Indochina watchers here add that a Burma-Cambodia mutual admiration society seems inevitable.

Said one: "If there are two countries in the world who want the world to stop so they can jump off, those are they."

Peking's drive to extend its influence in Southeast Asia and cool some of the border friction in the area grows from it s overwhelming desire to prevent regions instability that could be exploited by the Soviets, or by the Vietnamese.

Despite China's moral and economic support for Hanoi over the years, the Vietnam war did not do much for Peking's influence in the area, providng as it did the chance for massive introduction of Soviet arms.

For all their efforts to shore up the existing regional governments against Soviet and Vietnamese intrigue, the Chinese also must wrestle with accusations from the left-wing of international communism, such as Albania, that they are neglecting their obligation to promote world revolution. This may explain in part the unexpected congratulations to the Thai communists and the trouble the Burmese government has had this year with Chinese-aided rebels along their common border despite a series of warm exchanges between Peking and Rangoon.

This sort of two-edged foreign policy was teh brainchild of the late seems bent on following that lead. In the course of developing their relations with the new government in Cambodia, the Chinese have managed to finesse their longstanding ties to Prince Noredom Sihanouk, the former monarch who seems to have been shunted aside by hard-nosed revolutionaries like Pol Pot.

Peking recently published a warm from letter Sihanouk to the Cambodian party, one of the few signs that Sihanouk is still alive.

The Thai government seems to welcome China's efforts to end Thai come China's efforts to end Thai-leaders have apparently cooled relations with Taiwan.

The Chinese continue to make little headway with the Vietnamese despite ongoing economic exchanges and regular diplomatic dealings Hanoi recently chided Somalia for breaking with the Soviet Union, a split that Peking had warmly applauded.

The question of who is to control certain potentially oil-rich South China Sea islands still remains unsettled, Vietnam's Le Duan went so far as to lecture Hua during his visit on China's "international obligation" to held Hanoi recover from its war with the United States, and got for his trouble less than the usual warm Chinese reception or fellow Communists.