The new $654 million hospital at Chicago's Rush University Medical Center, which opens to patients Jan. 9 and is known simply as "The Tower," promises to be different. It already can be described as a powerful work of architectural sculpture, the curving profile of its glistening white bed tower soaring along the Eisenhower Expressway. It could be Chicago's next great building. But any assessment must remain provisional until doctors, nurses and patients inhabit the building and determine whether it is a triumph of function as well as form.