Reflecting a major shift in China's strategic alignment, Communist Party Chairman Hu Yaobang was sharply critical of the United States in his address to the national Party Congress here.

In his speech on Wednesday, Hu discarded the idea of an alliance with the United States as a global partner against the Soviet Union, according to excerpts released today.

Hu called Washington and Moscow equal threats to world peace, claiming that both are bent on "global domination." He portrayed China as seeking to unite with the Third World to "upset the strategic plans of the superpowers."

Hu took a slightly softened approach toward Moscow, recalling past friendship between the two Communist powers. But he renewed demands that Moscow must take "practical steps" to reduce its threat to China's borders as a prerequisite to any moves toward normalization.

The speech marks a sharp break from Peking's central diplomatic theme since 1977: That Moscow poses the greatest threat to world peace, and the only way to confront the Soviet menace is for China to join the United States and its industrialized allies and the Third World in an anti-Soviet coalition.

Although China's official media recently have increased their criticism of U.S. arms sales to Taiwan and of Reagan administration policies toward the Third World, Hu's address to the full meeting of Communist Party leaders is the first concrete sign of a high-level Chinese decision to distance itself from Washington.

"China never attaches itself to any big power or group of powers, or yields to pressure from any big power," Hu said, underlining this independent stance.

Hu also told the congress that China will abolish the post of Communist Party chairman as part of efforts to emphasize collective leadership, Reuter reported. The New China News Agency Sunday quoted Hu as saying that the party in future would be headed by a general secretary responsible to the political bureau. Diplomats had predicted the move and said Hu was certain to become the new general secretary.

Diplomatic analysts said that the address -- the most authoritative Chinese foreign policy statement in years -- reveals a fundamental change in both Peking's assessment of the Soviet Union as a security threat and in its view of Washington as a useful strategic partner.

Chinese leaders apparently have decided that positioning China between the two superpowers enhances its maneuverability and bargaining position with both of them, according to diplomats.

Peking has been reassessing its American connection for the past year, while diplomatic relations came close to retrogressing over U.S. arms sales to Taiwan. According to Peking, the U.S. refusal to stop supplying weapons to an island that Peking considers part of China displays an arrogant interference in Chinese domestic affairs and smacks of "hegemonism" typical of the Soviets.

China apparently also has concluded that identifying itself with the United States thwarts its efforts to block Soviet advances in the Third World. U.S. support for Israel and South Africa drives Arab and African countries closer to the Soviet Union, according to Peking's analysis.

Hu picked up this theme, saying it was "with the support and protection from U.S. hegemonism" that Israel carried out "its heinous aggression and atrocities" against the people of Palestine and Lebanon.

Although several months ago the official press here began to label U.S. diplomatic behavior as "hegemonistic" -- a derogatory term for aggressiveness that previously was reserved for the Soviet Union -- Hu went further in blurring the distinction between superpowers.

"In their pursuit of global domination," he said, "the superpowers have been contending on a worldwide scale with military power far exceeding that of any other countries. This is the main source of instability and turmoil in the world."

Coming almost three weeks after Peking and Washington agreed on a formula to defuse the Taiwan issue, Hu's speech suggests that the rhetorical hostility Peking had displayed during the negotiations was part of a general shift in policy and not, as some diplomats had speculated, an effort to soften America's negotiating stance.

Hu said that bilateral relations can "develop soundly" only if Washington stays out of China's internal affairs. But, he noted, a cloud hangs over the relationship because of the U.S.-Taiwan Relations Act, which requires the U.S. government to provide for the island's defense needs.

Hu urged the United States to "strictly observe" last month's accord, which Peking -- but not Washington -- interprets as a U.S. pledge of an eventual cutoff in weapons sales to the island.

While separating China from the U.S. strategic orbit, Hu made no reference to the growing commercial ties between the two countries. Chinese leaders have expressed hopes of increasing U.S. technology licensing and investment.

Hu's caution was magnified in the portions of his speech that dealt with the Soviet Union, reflecting the ambiguity of China's recent posture toward its archenemy.

While dropping the charge that Moscow is the superpower causing the greatest international chaos, Hu listed several Soviet actions that he said "constitute grave threats to the peace of Asia and China's security."

Referring to recent Soviet efforts to improve relations, Hu said that moves toward normalization would be possible if Moscow first lifted the threat posed to China's security by Soviet troops stationed along China's northern border and in neighboring Afghanistan and by Soviet support of Vietnamese forces in Cambodia.