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.