Linda Hamilton, the buff action star, is studying Yiddish-language tapes. The image is startling for anyone who remembers her as Sarah Connor, the all-American waitress-turned-warrior in James Cameron's "Terminator" flicks. It's even more startling when you consider that the Yiddish is for a play, Lou Shaw's "Worse Than Murder: Ethel and Julius Rosenberg," which opens tomorrow at the Ventura Court Theatre in Studio City. Hamilton plays Ethel Rosenberg, who was strapped into the electric chair in 1953 and executed, along with her husband, for conspiring to pass atomic secrets to the Soviets. Sitting on a faded gold couch in the bland rehearsal space at the Court, the petite, smoky-eyed actress says even she was surprised she accepted the part. "I'd sworn off heavy roles since 'Terminator 2' because I was just so sick of playing these very earnest, strong women," she says. Instead, Hamilton did some acclaimed TV movies, films such as "Dante's Peak" and a comedy or two.