And in HoME VII, The Treason of Isengard on page 236, I found a remarkable note by the professor.
Could not Balrog be Saruman? Make battle on Bridge be between Gandalf and Saruman? Then Gandalf comes out clad in white
Quite amazing, huh? It appears then that Tolkien may not have minded the "wizard-fight" between Gandalf in Saruman that happened in the FotR film! The makers of the movie whether they know it or not were honoring the professor's early conceptions