Whenever television pays tribute to the Broadway musical, which it does periodically, the Broadway musical comes out looking glitzier than it really is.

The spangle quotient usually goes up several notches, dancing feet are replaced by dancing cameras and TV celebrities who really have no business singing a show tune lip-sync their way through the preordained show stoppers. Perhaps to reestablish some measure of authenticity, however, Ethel Merman is generally tossed in toward the end.

"Texaco Star Theater . . . Opening Night," (tonight at 8:30 on Channel 4) runs pretty much true to form. It's a splashy 90 minutes, decked out like an automobile showroom when the new models come out and populated by a cast that literally runs from A (Debbie Allen, Steve Allen and the orphans of "Annie") to Z (Zsa Zsa Gabor in wall-to-wall fur).

The program itself is a kind of alphabet soup; there's no discernible pattern to the songs, which, one gathers, are being sung because, like mountains, they're there. Still, television has devised less pleasant ways to while away the time. Among the 19 star turns, the following are noteworthy:

Bernadette Peters, looking more than ever like a Vargas drawing, doing a sexy/pouty rendition of "Broadway Baby" (from "Follies"), which is not the way that upbeat song is usually handled, but why not?

Placido Domingo, lending his soaring tenor to "Some Enchanted Evening" (from "South Pacific"). It may come out "Soam Inchanted Evening," but it's still swoon time.

Carol Burnett, sniffling "Adelaide's Lament" (from "Guys and Dolls"), arguably the best show tune ever written. Shouldn't someone get up a revival of that classic musical for her?

The cast from "A Chorus Line," kicking its way to a final fade-out, surely as potent an image as ever for the evanescence and glamor of Broadway.

Other moments are considerably less sublime. Joe Namath, in a pink blazer and white derby, lumbers through "If My Friends Could See Me Now" (from "Sweet Charity"), the proverbial bull in a china shop. Loretta Swit, platinum hair doused in blue moonlight, tries vainly to act "Bewitched, Bothered and Bewildered" (from "Pal Joey"). And in a medley from "Oklahoma," Pam Dawber and John Schneider prove they are pretty as store mannequins, perhaps, but also that they are just as vacant.

Between numbers, the cast members rub elbows, nibble hors d'oeuvres and trade quips at what is presumably a glittery opening night party, but shouldn't fool too many. Gabor, candor itself, reveals that "Annie" is her favorite musical because not only does that stalwart orphan get her hands on Daddy Warbucks' millions, but "she doesn't even have to marry him." Charles Nelson Reilly, never at a loss for a double entendre, bats his eyes and says he always wanted to play "Pal Joey," because "I just love heels." And Sammy Davis Jr. turns up here, there and everywhere, spreading his joie de cool but invariably giving the impression that he is horning in.

Fortunately, "Texaco Star Theater" -- the first reincarnation since 1955 of what was once TV's most popular variety show--moves along swiftly enough so that the lapses of talent and taste are not overwhelming. The show manages to touch base with 49 musicals from Ziegfeld's "Follies" to "Dreamgirls," thereby guaranteeing something for just about everyone. And at the end, Merman strides on for "Before the Parade Passes By" (from "Hello, Dolly!"). The old pipes may waver a bit these days, but she blasts away as if she were the Monitor shelling the Merrimack. The musical is the American theater's most confident achievement and Merman, by golly, remains its chief pitchwoman and priestess.