Juggling trade, aid and diplomatic good will, China has launched a wide-ranging foreign policy offensive in the Third World, where it believes the Soviet Union will mount its most important challenges in coming years.

Peking is pursuing the policy with an ecumenical flair, embracing Latin American generals and African Marxists. Chinese statesmen have traveled from Rangoon, Burma, to Buenos Aires hoping to block or at least neutralize Soviet influence.

Although China regards itself as a Third World nation and has long played an active role in Asia and Africa, it has devoted its diplomatic energy in recent years to building an anti-Soviet coalition with Japan, Western Europe and the United States.

Having secured those strategic ties, China set out to renew its Third World credentials last year, accelerating the process after Secretary of State Alexander M. Haig Jr. met with Chinese leaders here two months ago.

The Haig visit produced mixed results. It advanced Sino-American relations by producing Washington's offer to sell arms to Peking. But the relationship continued to stumble over the unresolved issue of U.S. policy toward Taiwan.

Since then, Peking not only has shifted its diplomatic focus from the West to the Third World, but also has sharply criticized Washington for driving Arabs, Africans and Asians into the Soviet fold by supporting "reactionary governments" in Israel, South Africa, South Korea and Taiwan.

Although some diplomats believe the diplomatic offensive foreshadows a new Chinese alignment with the Third World and independence from the West, most analysts have concluded that the attacks against Washington were simply intended to boost China's stock among developing nations where American influence is low.

"The Chinese are trying to be friends with almost everyone but not depending on any one of them," observed a Western diplomat. "They want a broad enough relationship with the outside world to weather ups and downs with one particular country and still meet any Russian challenge."

An African envoy here who has frequently warned the Chinese about their loss of standing in the Third World because of their American ties said, "China is now trying to tell us that there's a difference between Washington and Peking."

Peking's new emphasis on the Third World springs from its view of the Soviet Union as the devil incarnate bent on dominating the world by encircling China and cutting off the West from vital natural resources, especially oil.

"The Chinese philosophy in the Third World is simple," said an Arab diplomat: "Whatever is Russian is no good. Whatever isn't, can be looked at as good."

Peking feels especially vulnerable in the Third World, fearing Soviet advances in the strategically important Indian Ocean and Horn of Africa as well as the Persian Gulf.

The Soviets, according to Peking, already have threatened China's security by occupying neighboring Afghanistan and by giving arms to Vietnam to challenge China's southern border and prop up an anti-Chinese government in Cambodia.

"The Soviet Union takes the United States as its main contender and Europe as its strategic point of contention," declared the Communist Party newspaper People's Daily last month. "However, for some time to come, it will take the crucial areas in the Third World as the main areas in which to expand its strength."

Peking began formulating a strategy to meet that challenge last year, according to Third World diplomats, and devised a policy that varies according to Peking's distance from the developing nation involved.

The offensive is marked by the flexibility that has characterized China's diplomacy in recent years, enabling Peking to sue for peace with India while renewing military aid to Pakistan, to pledge to withhold material support from communist insurgents in Southeast Asia while arming Khmer Rouge guerrillas in Cambodia, and to denounce Israeli militarism while helping to build Zaire's Navy.

Within its own back yard, China works closely with friendly Asian neighbors, using military assistance and diplomatic leverage to offset what it views as direct security threats from Soviet troops in Afghanistan and their proxies in Vietnam.

Peking supplies weapons to Khmer Rouge insurgents fighting the Vietnamese troops in Cambodia while supporting diplomatic moves by noncommunist nations in Southeast Asia -- including the recent United Nations conference -- to put pressure on Hanoi.

Chinese Premier Zhao Ziyang is now on a tour of Malaysia, Singapore and the Philippines, where he is expected to discuss regional efforts to nudge rival Cambodian rebel groups into a "united front."

Zhao also is expected to renew China's pledge to restrict its relations with outlawed communist insurgents in Southeast Asia to "the political and spiritual level." Since China first made that promise in Rangoon six months ago, the communist parties of Burma and Thailand have offered to negotiate with their governments. Malayan Communists are reported to have stopped using China as a base for their clandestine radio station.

China's new Third World offensive has included initiatives in stormy South Asia, where the Soviets have an estimated 85,000 troops in Afghanistan and exert influence over India through a 1971 friendship treaty as well as with trade and defense supplies.

In late June, Foreign Minister Huang Hua became the first Chinese official to visit India since 1960. He left with an agreement to hold early negotiations over the long-deadlocked border dispute remaining from the 1960 Sino-Indian war.

Huang also became the first Chinese leader to land in the Maldives, a strategically located island in the Indian Ocean, which earlier had rejected a Soviet offer to lease a former British air base there for $1 million a year.

Earlier in June, Zhao helped fine-tune China's relations with its principal South Asian ally, Pakistan. During a stop in Karachi, Zhao reportedly discussed the feasibility of sending arms through Pakistan to Afghan rebels fighting Soviet troops.

Zhao also renewed an old military assistance agreement with Pakistan, according to diplomatic sources. Although no official figures have been released, the Soviets say that the new pact calls for about $400 million in Chinese aid during the next two years.

When its security needs are no longer at stake, such as areas outside Asia, Peking competes for influence in the Third World with a mixture of economic assistance, trade and rhetorical support.

Whereas Chinese leaders of the 1960s called on revolutionaries in Africa, the Middle East and Latin America to overthrow colonial rule and oppose the United States, Peking has cut its ties with most insurgents there today. Nevertheless, it strongly supports the independence of Namibia (Southwest Africa) from South Africa.

In the African and Arab worlds, China has replaced its old radicalism with aid programs to 42 nations. Unlike the Soviets, who favor military grants and grandiose industrial projects, China concentrates on less dramatic programs, such as rice cultivation and road building.

When Zimbabwean Prime Minister Robert Mugabe visited China in May, he brought along most of his Cabinet to discuss aid projects. He left Peking with pledges of more than $70 million in economic and military assistance to his new Marxist nation, according to African diplomats.

In the Middle East, Israel has become one of Peking's favorite targets since the recent Israeli bombing attacks on Lebanon and Iraq. China strongly backs Palestinian rights, demands Israeli withdrawal from occupied territories and favors uniting of the Persian Gulf states into a cooperative unit.

In Latin America, China is moving to boost trade, which grew threefold between 1977 and 1979. Every year Peking imports about a million tons of wheat from Argentina and enjoys a brisk trade with Brazil, Mexico and Peru.