Coincidentally, American Movie Classics has commissioned a new compilation documentary for the holidays, "The Great Christmas Movies," which devotes a segment to "Meet Me in St. Louis," memorably contrived to be both a Halloween and a Christmas classic. An interiew with Margaret O'Brien, the once-phenomenal child star who played Miss Garland's kid sister, supplements this interlude. TCM also has "Meet Me in St. Louis" on its December schedule, with showings next Sunday and Christmas Eve.

The bound version of "Christmas Movies" also includes additional reminiscences with Miss O'Brien. For some reason, author Frank Thompson, who also supervised the special, has failed to incorporate the most amusing recollection from the book in his TV footage. Did it get lost or ruined in the lab?

Mis O'Brien denies the venerable tale that Mr. Minnelli induced her to cry hysterically during the pivotal Christmas scene by resorting to a tactical lie: the claim that her dog had died. Miss O'Brien argues persuasively that this was a legend commonly associated with Jackie Cooper when he was a child star. Moreover, her mother never would have played along with such a mean fib.

However, her mother was not above appealing to little Margaret's professionalism and competitive pride. She urged her daughter to trump June Allyson,, also known around the MGM lot as a virtuouso weeper, by playing a crying scene to the hilt. This devious show-business mom made the idea of falling back on the application of artificial tears seem shameful. The argument evidently worked wonders- and makes for a better legend, provided one is familiar with the rival actresses.