RAMBLING ROSE, with Laura Dern (left), Robert Duvall, Diane Ladd and Lukas Haas. Directed by Martha Coolidge. At Cine-Art. WHAT with Driving Miss Daisy, Fried Green Tomatoes and now Rambling Rose, tales of the southern United States seem to be in vogue in Hollywood. Laura Dern is southern belle Rose, a charming 19-year-old whose desperate search for love has led her into the bed of many an unsuitable suitor. Rose, fresh from a brush with prostitution, arrives to work at the Hillyers' family home all apologies, gangly legs, and gratitude. She is guileless, a little too innocent for her own good and although well meaning, incorrigibly, undeniably sexual. Dern's portrayal of a young woman who exudes sexuality despite herself shows her to be a much better actress than was ever hinted at in films like Fat Man and Little Boy or the over-rated Wild at Heart. Rose is awkward and clumsy, but Dern turns these normally unattractive traits into something of a ballet hinting at enormous reserves of sexual energy. All of which might have been fine had Rose reached sexual maturity in 1975, but Rambling Rose is set in 1935 and the ex-farm girl's sexual activities become something of a problem for ''Daddy'', head of the Hillyer family. Daddy is played by Robert Duvall, a challenging part worthy of his talents. Daddy, having already been forced to fend off Rose's sexual advances (during a highly erotic sequence involving no explicit sex), is fully aware of Rose's desperate need for love but eventually he must make a choice: to keep Rose and try to help her, or to kick her out to safeguard the moral well-being of his children. If one discounts moments of over-sentimentality, Rambling Rose is an enjoyable film with a gratifyingly liberal sense of humour. It is this sense of humour that allows Rose to be promiscuous without seeming a slut, and innocent without ever coming acrossas dumb. Director Martha Coolidge is to be congratulated on the deft manner in which she controls that use of humour.