Last year Jeff Smith published an essay on David Bordwell's website Observations on Film Art: here is a link to "Spies face the music: Jeff Smith on FOREIGN CORRESPONDENT."
According to Smith, "if you want to get a handle on the basic features of the classical paradigm, Foreign Correspondent’s typicality makes it [very] useful as an exemplar. Newman’s music neatly illustrates several of the traits commonly associated with the classical Hollywood score’s dramatic functions." The essay is in fact a detailed enumeration and interpretation of leitmotifs. Despite being somewhat understated in many places, Newman's score is densely constructed with musical themes, and Smith does an excellent job of unraveling the complicated web of themes and their uses.
Note: The leitmotif is initially discussed in Chapter 5 of Hearing the Movies, under "Characteristic Music Practices in the Later Silent Era," pp. 121 ff.