Perhaps just to be cute, or perhaps just to amuse themselves while occupied with drudgery, the writers of "Legs," a new NBC sit-com, named its heroine Norma "Mama" Bates. Norman Bates was, of course, the fellow with the mama problem in Alfred Hitchcock's "Psycho." This may be neither here nor there, but neither is "Legs."

"Legs" has no relationship to "Jaws," either; essentially it's "Mrs. Blanksy's Beauties" without Mrs. Blansky Producer Garry Marshall created "Beauties" as a vehicle for Nancy Walker, and after the show flopped on ABC last year, he somehow sold NBC on the same idea with comedienne-singer Marcia Lewis in the maternal role. The result airs tonight at 8 on Channel 4. NBC bought the series on the basis of this pilot, and it is to begin in the fall.

Marshall's formula touch is evident; "Legs" is crawling with zany though uninteresting characters who work at a rundown Las Vegas hotel. Widow Bates is a tubby clown with a knack for poignant ballads and a 15-year-old son, played by the overly accomplished Scott Baio ("Bugsy Malone," "Happy Days"), who, in the premiere, arrives from New Jersey for a hectic new life with mom.

It's a crowded and predictable show, and director Alan Rafkin has a hard time pretending there's really a story to be told. The script, by Walter Kempley and Marty Nadler, is all wisecrack and retort until token heart-tugging prior to fade-out.

Naturally the setting lends itself to the display of spunky cupcakes in scanty showgirl duds, and though there's nothing wrong with that, the sonny-boy character is such a randy, voyeuristic little tyke - he "made passes at the waitresses" in a restaurant, we are told, kissing their "belly buttons" - that the lark frequently borders on the seamy.

Lewis has agreeable bounce, but the character to character and gag to gag to get her into focus, except during a concluding solo. Scenes are short and choppy, jokes and strained, and the true comic and dramatic potentials of the material ignored. TV writers don't need more money; they need more air. Meanwhile, we're the ones who get to suffocate.