Some items simply need no comment. The Mitchell Brothers, northern Californians who produce adult films, took out an ad in this Monday's Daily Variety, the entertainment trade paper. It reads: "Mitchell Brothers Film Group seeks dwarfs, midgets, fat lady and geeks for 'Behind the Green Door: The Sequel.' Frisco lensing set for March." Then a phone number and instructions: "Ask for Chico." End of ad. To Market, to Market By the way, if Chico or the Mitchell Brothers or any of their colleagues have come down from San Francisco to Los Angeles, they'd better stay away from the Beverly Hilton Hotel. That's the site of this week's American Film Market, a supermarket of independent films looking for distribution.

X-rated films are a significant part of that market, but they're not classy enough for the AFM's host hotel, which doesn't let adult films on the premises. Instead, the Beverly Hilton has rented space to the folks responsible for, say, "Private Property" ("Virgil was a virgin . . ."), "Hollywood Vice Squad," "Stitches" ("Malpractice Made Perfect") and "Unmasking the Idol," the tale of a suave adventurer and his trusty sidekick, Boon the Baboon ("Younger Than James, Faster Than Jones, Madder Than Max, Now Meet Duncan Jax!").

A slightly more refined gathering takes place tomorrow night to benefit the American Cinematheque, a film preservation and historical society recently formed in Los Angeles and now merged with L.A.'s Filmex festival. Some purists grumbled when it was announced that the organization's Moving Picture Ball would honor Eddie Murphy -- the theory being that a respected film organization ought to pick somebody a little older and less mainstream.

But the choice may have paid off: Late last week, the event was suddenly moved from an 800-capacity soundstage at 20th Century-Fox to a nearby hotel ballroom with about twice the capacity. It seems that Fox simply couldn't find room for all the folks who want to honor Mr. Murphy. Casting Call

A couple of this year's Oscar nominees are included in the cast of "Native Son," a planned film version of Richard Wright's 1940 novel of racial tension in the Northeast. Joining previously announced Oprah Winfrey from "The Color Purple" will be "The Trip to Bountiful's" Geraldine Page.

Other performers include Matt Dillon, Elizabeth McGovern and Carroll Baker; the director will be Jerrold Freedman, who usually works in TV. But then, "Native Son" is in a way an expanded TV movie: Like "Testament," it is part of PBS' "American Playhouse" series and will thus be shown on public television after its theatrical release but before it is issued on videocassette or shown on cable. At the Box Office

This is the crucial weekend for Woody Allen's "Hannah and Her Sisters," which spreads out to 400 theaters after doing terrific business in its far more limited engagements.

It's also the weekend we'll see whether audiences are ready for a third high school movie from director John Hughes and actress Molly Ringwald, who've followed "Sixteen Candles" and "The Breakfast Club" with "Pretty in Pink," in which Ringwald is torn between nerdy but endearing Jon Cryer and rich kid Andrew McCarthy.

Note: The one she winds up with isn't the one she wound up with in the original screenplay; the filmmakers reportedly decided that young audiences wouldn't buy Molly walking away from the guy she was supposed to walk away from. So some tinkering was done, and now Molly gets the more marketable of the two fellas, but she does so without making the other one mad at her. Neat trick.