Liberace separates the kitsch from the camp. He's priceless. Or expensive, anyway. "Liberace in Las Vegas," the special PBS will show as a fundraiser tonight, opens with film shot in Lib's house, scenes of the pianist waking in a canopy bed, pretending to tickle the keys of a piano cake, frolicking as best he can in a bubble bath, winking and twinkling to beat (with a fluffy pillow) the band.

He's perfection: show-business bad taste raised to the level of low art and flavored with a cuckoo, redemptive, doodly innocence. Assessing one of his innumerable ghastly costly costumes, he says to his Vegas Hilton audience, "Oh, I gotta tellya, her majesty -- you know, Queen Elizabeth? -- she loved it." There's something endearingly honest about phoniness so tenderly unaware.

The program, at 10:15 p.m. on Channel 26, represents a curious buy for public television. It's not exactly BBC. It's not even Thames or Granada. But then, whatever rules PBS plays by the rest of the time go out the window during pledge-break plagues. One wonders, do the viewers who are inspired to phone in donations by the sight of a Liberace nightclub revue or a creaky big-band bash really think they'll be getting this kind of programming 52 weeks a year on public TV?

Not only is the Liberace special questionable public TV fare, it's a virtual antique by TV standards. The program was taped for pay-ca-ble four long years ago. Much has happened since. During the show, Liberace says he'll be passing one of his costumes on to brother George, but brother George died in 1983. Worse (or better, depending on one's appetite for the grotesque), Liberace asks the crowd to applaud the chauffeur who drives him onstage, identifying him as "my friend over there," Scott Thorson.

In October 1982, Thorson filed a multimillion-dollar palimony suit against Liberace, claiming to have been thrown out of Liberace's L.A. penthouse after six years of an "intimate, sexual, emotional and business relationship." This puts something of a pall over the two appearances by Thorson on the special, and over Liberace's mock flirtations with women in the audience.

You don't want to see Liberace picked on. There's a fragility there. And so running this special now seems to open him to ridicule, and is therefore a little cruel.

Apparently Liberace has spruced up his act since this performance was recorded on tape. It's not as gushingly spectacular a show as one may hope for, although the entertainer's recent Radio City Music Hall appearance reportedly was. In this Vegas turn, he's abetted by the Ballet Folklorico of Mexico, a rather incompatible diversion, and the Dancing Waters, streams of multicolored whoosh that sway and spurt roughly in time with the music. Tacky, but not quite tacky enough.

Thomas V. Grasso's TV direction isn't tacky, just terrible. The camera shots and angles are so routine and dull witted that the program looks as if it was taped on autopilot. There couldn't have been a human in the booth. While Liberace is playing a relatively sensitive "It's Impossible," a long shot reveals that people in the foreground are getting up and leaving. Sad. And on the part of the director and editor, inept.

Liberace's numbers are mostly medleys -- "A Musical Salute to Our Friends South of the Border" and a Johann Strauss montage that opens with a bombastic snippet of Richard Strauss' "Also Sprach Zarathustra" -- and his style remains a mad melange of showy arpeggios and glitzy glissandos. He cues the audience to applaud so often that it's no wonder they look a little pooped at curtain time. "Well, look me over. I didn't get dressed like this to go unnoticed," he says. "Do you like it?" Then he twirls in his cape while they clap clap clap. Later: "My 35th year in show business. What do you think about that?" And, amid encores, "More? Okay!"

Of course they'd applaud if he said it was his 14th day in show business. What do you think about that? Whatever the indignities rendered Liberace by the airing of this special, one does like to think he has the last laugh, or at least the last grin. "Remember that bank I used to cry all the way to?" he asks the audience. "I bought it. Ha ha ha ha!" At the very end, while the last music is playing and the audience is bleeding the last drops of applause from its hands, Liberace flies, literally, above the stage. A wire hoists and dangles him. It's one of the dumb-loveliest things you've ever seen.

In fact, it's not too tacky for public television. It's too good for public television.