7PM This episode's headline: Li Peng: Man of the Future; A Fighting Vehicle; Budget Battles; Japan in Tennessee. The guests include In Chicago: LI PENG, Vice Premier, People's Republic of China; In Washington: COKIE ROBERTS, National Public Radio. Byline: In New York: ROBERT MacNEIL, Executive Editor; In Washington: JIM LEHRER, Associate Editor; JUDY WOODRUFF, Correspondent