NEW YORK — Her heart may belong to the U.K., but this season, London-based Luella Bartley is rooting for the U.S.A. In her second runway show here, the designer served up a slice of Americana with a lineup of classic sportswear loaded with a hip, Seventies sensibility. Inside-out sweatshirts, oversized cuffed corduroy pants and, of course, lots of denim were some of her hot items. Here, her cavalry-style minidress. For more on the New York show season, see pages 4 and 5.