Alfred Hitchcock once told Peter Bogdanovich that the problem with his penal-colony melodrama was its casting. He'd wanted Burt Lancaster for the rich ex-con in 1830s Australia played by the more decorous Cotten: ''The character should have been a horny, manure-smelling stable hand.'' Okay, but Bergman, doing her hysterical thing, is nearly self-parodic as his wife -- a delicate flower wilting Down Under. Pitched somewhere between stagy gothicism and corny weepie-dom, Under Capricorn is just plain soporific. Question for film students: Why couldn't Hitch make a decent period piece? EXTRAS None.