Faced with composing a new Star Trek theme for the film, Goldsmith initially struggled for inspiration, and proceeded to compose as much of the score as possible before the need to develop the main title theme. His initial score for the scene in which the newly-refit Starship Enterprise is revealed to the audience was not well received by the filmmakers, director Robert Wise feeling that it lacked a strong thematic hook and evoked sailing ships. Though somewhat irked by its rejection, Goldsmith consented to re-work his initial idea and finally arrived at the Star Trek theme which was ultimately used.

Jerry Goldsmith - Wikipedia

The theme is distinct. I had always correlated the theme with TNG until I watched The Motion Picture several years after TNG. I did not recognize that the theme was used in both. It's amazing because it almost didn't exist, and was composed after pretty much the rest of the score was complete. Goldsmith had to rework it because the director wanted a "strong thematic hook."