This fall's onslaught of Mafia movies has not gone unnoticed by the video studios, which have vaults full of vintage gangster films that have yet to be released. While it never built a reputation in the gangster genre to equal that of Warner Bros., Twentieth Century Fox may have the largest lode of untapped Mafia movie wealth, as various licensing arrangements with other studios allowed its video subsidiary CBS/Fox Video to leave its library alone until recent years. Now the folks at CBS/Fox are bringing more Fox classics to the video market, category by category, and are best positioned to take advantage of the current appetite for organized screen crime, whetted by the promise of "Godfather III's" imminent arrival in theaters.

Just this week Paramount made it official that "Godfather III" will be released next month. That will coincide with "Great Gangsters," CBS/Fox's four-title salute to the days when crime and punishment ruled the nation's marquees. While none of the four movies is as conspicuously concerned with the Mafia-variety gangster as "GoodFellas" and other current hits, all are making their home video debuts. Forming the gangsterama are "Kiss of Death" (1947), featuring Richard Widmark in his film debut as a thug who in one memorable scene pushes a wheelchair-bound woman down a flight of stairs; "Seven Thieves" (1960), starring Edward G. Robinson and Joan Collins; Elia Kazan's "Panic in the Streets" (1950), with Widmark as a medical examiner trying to halt the spread of a bubonic plague in New Orleans; and Joseph Mankiewicz's "House of Strangers" (1949), with Robinson and Susan Hayward in turn-of-the-century New York costumes.

CBS/Fox has priced the foursome at $39.98 each -- low enough, it hopes, that even conservative video rental retailers will take a chance that old crimes do pay. Season's Greetings

Perhaps studio executives were impressed by the consistently jolly sales of classic Christmas movies on cassette; maybe they just wanted to create new holiday heartwarmers to feed the seasonal market in future years. Whatever the reason, that old studio standby has enjoyed a slight renaissance in recent years.

Last year saw the big-screen release of two major Christmas-themed movies: "Prancer," which was aimed directly at the kids-and-carols set; and "National Lampoon's Christmas Vacation," which parodied all of the forced good cheer that "Prancer" sought to exploit. The split sides triumphed over the warm hearts, and "Christmas Vacation" topped the box office chart during last year's holiday weekend. So timeless was "Vacation's" humor, in fact, that the film enjoyed off-season rental success last spring.

Now the two are back in competition again: "Prancer" hits the video rental market next week from Orion Home Video, and a $19.98 edition of Warner's "Christmas Vacation" will show up on discount video shelves the following week. The longest-running series of Christmas films, meanwhile, will add one more movie to its collection late next month when LIVE Home Video unleashes its rental market entry "Silent Night, Deadly Night 4: Initiation" -- the second film in the controversial series to bypass theaters and go directly to home video. According to LIVE, the film involves a Devil-worshiping cult whose members are promised immortality; apparently "It's a Wonderful Afterlife" was too tasteless a title even for them. Pirates Beware

Moviegoers who stumbled unprepared into a screening of the audience participation favorite "The Rocky Horror Picture Show" likely thought they were seeing one of the strangest film experiences ever. Consumers who rent or buy their copies of "Rocky Horror" when it reaches stores next week will see some of the strangest-looking tapes they've ever seen -- before they even put them in the VCR. CBS/Fox has come up with an unprecedented number of distinguishing features for its "Rocky Horror" cassettes, including: a black cassette shell with bright-red shell door; a laser-marked "RHS" burned into each shell door; special multicolored cassette labels, and an additional cassette marking that won't be announced until days before the tape's release. All of which, along with standard Macrovision copy protection encoding, is designed to prevent amateur and professional pirates from making and marketing illegal copies of the tape, long a favorite among video black marketers. So much for audience participation.