CHINA'S Communist Party yesterday marked the hundredth anniversary of the birth of its most famous leader, Mao Zedong, by unequivocally linking the Great Helmsman to the ''New Helmsman'', Deng Xiaoping. In a one-hour speech to an audience of 10,000 invited guests in Beijing's Great Hall of the People, party General Secretary Jiang Zemin repeatedly spelled out how Mr Deng's reformist policies were the logical extension of Mao's authoritarian brand of socialism. Chairman Mao had made several ''leftist'' mistakes in his later years but these had been corrected after Mr Deng came to power in 1978, Mr Jiang said. Mr Jiang's speech, made in the Great Hall's main auditorium beneath a huge portrait of Mao and a front page editorial of the People's Daily , seemed designed to reclaim the party's great revolutionary hero and thereby legitimise the current leadership's policies. ''The best way to remember Comrade Mao Zedong is to be guided by [Mr Deng's] theory of building socialism with Chinese characteristics . . . and to keep pushing forward the cause established by Mao and the old generation of proletarian revolutionaries,''Mr Jiang said towards the end of his speech. Although the speech was ostensibly about Chairman Mao, the bulk of the address was devoted to Mr Deng and his contributions to the development of China since the death of the Great Helmsman in 1976. The New Helmsman was the natural heir and successor to Mao, Mr Jiang said, without mentioning the fact that Mr Deng had been purged twice by Mao during the Cultural Revolution. ''Comrade Deng Xiaoping and Comrade Mao Zedong are the same in that they always opposed the abstracting of Chinese society and the reality of the Chinese revolution and construction in the study of Marxism,'' he said. Dressed in a formal dark blue Mao suit, the party secretary was so keen to emphasise the link between Mao and Mr Deng that he got his leaders mixed up at one point. ''Mao Zedong,'' Mr Jiang (Cont'd from Page 1) began, before realising his mistake, ''Deng Xiaoping led our party and state in shaking off the disaster created by the Cultural Revolution,'' he continued hurriedly. The continued stress on Mr Deng's achievements apparently became too much for former president Yang Shangkun, who, after sitting next to his old revolutionary comrade Bo Yibo for about 10 minutes, got up and walked off stage behind Mr Jiang. No reason for Mr Yang's sudden departure was given but there was speculation that the former president, who was sidelined by Mr Deng last year, could not bear to hear Mr Jiang sing the praises of the patriarch any longer. Although the party secretary mentioned Mao's mistakes in his later years, the emphasis was always on his achievements in leading the communist revolution. Mr Jiang quoted Mr Deng as saying that Mao's mistakes were secondary to his ''meritorious achievements'', and that his mistakes were a result of departing from his own correct principles. ''The mistakes he made were those of a great revolutionary and a great Marxist,'' Mr Jiang said. Following the ceremony in the Great Hall, the party's leaders, without Mr Yang, made their way over to the Mao Zedong Memorial Hall in Tiananmen Square next door to pay their respects to the Great Helmsman. The Politburo, led by Mr Jiang, bowed three times before the huge marble statue of Mao in the entrance to the mausoleum. They filed silently past Mao's mummified body, followed by other ''old revolutionaries'' and the late chairman's relatives. Apart from a road race for amateur athletes around the party's headquarters in Zhongnanhai, there were no popular commemorative activities in remembrance of the man Mr Jiang said the Chinese people loved and respected so much.