X MARKS THE PLOT

20th Century Fox executives may not want you to know it, but the mysterious title of their big Christmas entry, “Project X,� was once what it sounds like--a working title.

We called about the vagueness of the title, mentioning marketing problems that beset Orion’s “F/X� (now called “Murder by Illusion� for European release). But Fox brass had a only a curt reply: “We respectfully decline comment on the matter.�

But screenwriter Stanley Weiser confirmed our suspicions: “(Co-producer) Larry Lasker jokingly wanted to call it ‘Project X’ (as a temporary title) and it stuck.�

The movie, still shooting, has Matthew Broderick as an airman assigned to a hush-hush military training program. He befriends a smart chimp, whose use of sign language reveals the sinister secret.