A search for the cultural legacy of Chairman Mao Tse-tung in mainland China is the focus of one of the best documentaries in the ''Frontline'' series. It constitutes firm evidence of the long-range value of TV's only weekly documentary series.
Looking for Mao [(PBS, Monday, 8-9 p.m., check local listings for premiere on various days and for repeats)] seems to be a straightforward attempt by documentary-maker Irv Drasnin to study the long-term effects of the Cultural Revolution of the 1960s and '70s. Interviewed are students and ordinary citizens of China who look back in wonderment - and some bewilderment - at the period not long ago when there were only eight officially approved ballets and operas, when all foreigners and things foreign were vilified, when many intellectuals were banished to rural farms.
Those interviewed now seem to believe that today's China understands that personal goals must be satisfied as well as state goals, that freedom to think is essential, that ''if we work hard we can get a good life.''
One major weakness of the film is that so many of those interviewed were obviously an English-speaking elite; the tight Chinese controls make real man-in-the-street interviews an impossibility. So students make up most of the talking heads - albeit fascinating talking heads.
Some Chinese who appear in this film say they are aware of the danger of over-Westernization. They worry about the tendency among the young to try to adopt everything in Western life without understanding that Eastern attitudes must be preserved.
Producer Drasnin admits that there is an element of unfairness in his report. After all, ''Mao is being judged by his victims,'' it is pointed out. But in general, the film finds that although most Chinese are grateful to Mao for some things, they are not at all grateful for the Cultural Revolution and the reign of terror of the Red Guards. The Maoists? They wait silently, not really convinced of the new road to socialism.
One of the most moving moments in this incisive quest for truth is a sequence in which a young Chinese student recites Martin Luther King's ''I have a dream'' speech and then links arms with his fellow students as they all sing ''We Shall Overcome.'' A whole new generation of Chinese, it seems, understands the battle for freedom.