THE few mainland Chinese films released here seem to be either leaden historical epics of communist history, second rate imitations of Hongkong action pictures or more personal portraits of diverse aspects of contemporary life. Stand Up, Don't Bend Over belongs in the third category. This Xi'an Film Studio production is a droll, insightful look at various strata of society battling it out in the rough-and-tumble 1990s. The protagonists are three neighbours - an intellectual, a party cadre and a hooligan-turned-entrepreneur. Huang Xin's screenplay sketches a perceptive and witty picture of the trio and their families. Businessman Zhang (Niu Zhenhua) is a coarse lout, a bully with no regard for anything but his financial gain. But by the end, you cannot help having a grudging admiration for the way he manages to meet each crisis and adapt to changing circumstances. Cadre Liu (Da Shichang) is neither the caricatured functionary of Hongkong movies nor the upright revolutionary seen in countless mainland productions. He is a mild-mannered ''company man''. The trouble is, his company no longer enjoys the prestige it once had. Author Gao (Feng Gu) is the film's focal point, someone respected by both the barely-literate money-maker and the officious commissar. But Gao's is also a precarious existence, literally wedged between the almighty dollar and the even mightier party. Throughout, director Huang Jianxin applies the same fresh point of view and sense of humour that marked his Black Cannon Incident as one of the highlights of Chinese cinema in the 1980s. Stand up, Don't Bend Over doesn't pretend to make a grandiose statement about China in the '90s, but has fun painting a portrait of a society in the throes of trying to define what ''socialism with Chinese characteristics'' really means.