Diana Ross spends most of her 90-minutes NBC special Sunday night posing for Vogue covers and accepting the ovations of an audience so hammily demonstrative that it puts the crowd on "The Price Is Right" to shame. They love Diana, Diana loves them, and viewers may begin to feel like voyeurs.

"An Evening with Diana Ross," the "Big Event" on Channel 4 at 9:30 p.m., turns out to be one of the year's more enjoyable disasters. The execesses are so excessive and the vulgarity so consistent that the show becomes an entertaining shambles. It's on the maddening side, but it's also pretty irresistible.

The program is so poorly directed and so clumsily edited that when it's all over, you're not sure Ross has ever quite been in focus or sung a single song all the way through. But then, the implicit point of the ceremony is that Ross's songs are now all really little parts of One Great Song, the Ballad of Diana Ross, and just about every number is a number about her career, her ascendancy to living legend, and her troubled search for identity amidst the deafening hurrahs of fans.

A wretchedly assembled retrospective on Diana Ross and The Supremes has Ross narrating film clips of the group with sarcastic asides, as if the team were a joke and merely an incubator for the splendiferous superstar who would emerge later. For one, or maybe two, generations, this kind of dismissal is virtual sacrilege.

What we are watching is the coagulation of myths about modern mythmaking in mass media America. It's getting much easier to be a myth, and there's a kind of mythspeak that, once mastered, can weather a performer through almost any calamity. It seems to be weathering Ross not only through such movies as "Lady Sings the Blues" and "Mahogany" but also through this TV show, which is really a homage to homage, a high mass for star worship.

The coup de grace comes when Ross portrays Ether Waters, Bessie Smith and Josephine Baker, who drop by not to sing but, in a gesture of virtually celestial gratuitousness, to bolster the morale of Diana Ross. It's like sending diamonds to Zsa Zsa.

There are some helplessly charming moments on the show. The Supremes footage fades into Ross singing "What I Did for Love," and the sentimentality is overwhelmingly affecting. Ross sings several other songs which, like "Love," are from the score of "A Chorus Line," and in fact she sings to many of them that she may be auditioning for a part in the movie version. Or maybe she is auditioning for all the parts in the movie version.