ONE of the last, lingering images in 'Mississippi Blues, is that of an elderly black man playing a homemade flute while sitting on a weather-beaten, horse-drawn wagon. The man is surrounded by a French documentary crew, also seen on camera, which records his every move as though no horse, wagon or blues musician had ever before been captured on the screen. 'Mississippi Blues,' amiably follows Bertrand Tavernier's expedition through the rural American south, capturing both the naiveté and the fascination Mr. Tavernier brought to this expedition. His partner in the venture, the American film maker Robert Parrish, tempers the French visitors' taste for tourism with a wry perspective of his own. Mr. Parrish, who was born in Georgia, and his longtime friend Mr. Tavernier study banyan trees in one scene, for instance, and Mr. Tavernier is reminded of an image in a Nicholas Ray film. Mr. Parrish says that he, too, finds the trees evocative, but adds 'I just don't want to have them the only thing in our picture.' There is no danger of that, since 'Mississippi Blues' contains an abundance of jubilant music and lively, talkative local characters. Aside from the obligatory kudzu, highway signs, burger joints, landmarks (Faulkner's tombstone) and odd bits of information (Coca-Cola was first bottled in Vicksburg), the film contains a great deal of vibrant, homespun music. A gospel choir is heard rehearsing rousingly in church; a barber (working in a combination bar-barbershop-pool hall) sings while he shaves Mr. Tavernier with a straight razor. The occasional expert is also heard from; a poet and a sociologist are both solemnly interrogated by Mr. Tavernier - but the film's real strength rests on sheer personality. One man's instructions for finding, catching and cooking a possum are particularly memorable, although Mr. Parrish's accompanying enthusiasm (he says the whole thing is making him hungry) seems less authentic. In any case, 'Mississippi Blues' manages to be both serious and quaint in equal measure. And all of it has an easy spontaneity and good cheer. MISSISSIPPI BLUES, a film by Bertrand Tavernier and Robert Parrish (in French with English subtitles); cinematography, Pierre-William Glenn; edited by Ariane Boeglin; produced by William Ferris; Running time: 96 minutes. This film has no rating.