Hu Yaobang moved today in his first speech as China's Communist leader to unify the nation's ruling party after months of bitter infighting and two days of the most dramatic political changes since the death of Mao Tse-tung.

In an address marking the party's 60th anniversary and his second day as chairman, Hu appealed to his old leftist enemies to put aside their grudges and to unite behind the pragmatic policies that have guided the nation since Mao's death in 1976.

"The best way for us to celebrate this grand festival, the party's birthday, is to learn from historical experience and thus unite and look forward, focusing our attention on unresolved problems," he said at a rally in the Great Hall of the People.

The conciliatory gesture came after months of splintering debate that ended this week with the party's decision to criticize formally the radical policies of Mao, its founder and first chairman, and to replace his personally chosen successor, Hua Guofeng.

For Hu and his fellow party moderates, the nationally broadcast speech represented a crowning moment, a public demonstration of the victory they have sought in internal political struggles for years, decisive control of the powerful party apparatus.

Vice Chairman Den Xiaoping, 76, the pragmatists' leader who has worked for years to install a team of like-minded modernizers to carry on his programs, sat on the speakers' stand to the left of his old friend Hu, attentively listening to his words.

Another Deng favorite, Zhao Ziyang, stood to Hu's right, reflecting his importance in the new party lineup. Zhao replaced Hua as premier last September and was named as party vice chairman Monday night, a position ranked fourth in the Communist hierarchy.

Several seats down sat a dejected Hua, 61, who was dropped from the party's top post to lowest ranking vice chairman and severely criticized for clinging to Mao's principles of political activism and radical economics after Hua became chairman in 1976.

With Zhao, 62, running the government and Hu, 67, heading the party, Deng has positioned men whom he can trust to prevent a return of Maoism and to continue Deng's economic modernizaton and pro-West foreign policy after he dies or retires.

Deng was able to elevate Hu and get the party to rebuke Mao only after months of bitter infighting, pitting the moderates against cadres who prospered during Mao's era and now fear that condemning him threatens their current positions.

In the most pointed portion of his generally mild speech, Hu issued a warning to official who implement policy who in recent years have blocked Deng's reform measures because of their loyalty to Mao and their hope for a return of Maoism.

"Comrades at a lower level must respect and obey the leadership of comrades at a higher level," said Hu. "They must not feign compliance while actually violating or resisting instructions from the higher level."

The speech, however, made it clear that the new leaders plan no purges of leftists who comply with the new line.

"So long as the comrades concerned have recognized their mistakes and are willing to correct them," said Hu, "we should encourage them to go on working boldly."

This apparently was designed to allay fears of party officials who started their careers as leftists. As many as half of the Communist Party's 39 million members joined during Mao's Cultural Revolution of the late 1960s, which was harshly criticized this week.

In the spirit of conciliation, Hu noted Mao's achievements as a revolutionary leader and thinker. The new party line adopted this week was that Mao did more good than bad and called him "the greatest national hero in Chinese history."

Although Mao and the party made serious mistakes, he said, it is time to put them aside because "the internal unity of the party and the party's unity with the people are the essential condition for the triumph of our cause."

Mixing Maoism with his own brand of politics, Hu concluded his 100-minute speech with a call to the party "to unite under the great banner of Marxism-Leninism and Mao Tse-tung thought and boldly labor to make China a modern and powerful socialist country, a country that is properous, highly democratic and culturally advanced."