Actress Ruta Lee is acting as a one-woman conduit to help her Lithuanian relatives emigrate from the Soviet Union. Lee has thus far brought her grandmother and a cousin over to this country; the cousin, Maryte Kaseta, arrived Wednesday. "Everyone laughs here," said the 18-year-old Kaseta, speaking in Lithuanian interpreted by Lee. "In the Soviet Union, people don't laugh so much. They are more cautious." In 1964, Lee succeeded in a 12-year struggle to bring her 90-year-old grandmother from Siberia to the United States.