Vice-Premier Deng Xiaoping is pushing to oust Hua Guofeng from the Communist Party chairmanship, possibly before the end of the year, diplomatic sources said. They said Mr. Deng is spearheading the campaign by the ruling hierarchy to dump Mr. Hua, who was the handpicked successor of Mao Tse-tung. His plan apparently involves replacing Hua with Hu Yaobang, who handles the party's day-to-day affairs as secretary-general of the Secretariat. Mr. Hu has already been performing some functions once reserved for the chairman. He hosted Communist Party delegations from Spain and Italy and made several key policy speeches. Mr. Hua, who has dropped from sight, resigned from the premiership in September.