In the light of President Nixon's historic visit, what is modern China actually like? In April ithis year, MAX HASTINGS and a camera crew from 24 Hours walked across the Shumchun bridge from Hong Kong into China. After five bitter years of private turmoil, China had thrown back the shutters and opened the nation's door -at least a crack-to an ever-fascinated outside world. Initially Hastings was invited only to cover international table-tennis, but was later given permission to travel extensively within China and to bring back these glimpses of life on the other side of the bamboo curtain. Producer William AARON