"Evita," the Tim Rice - Andrew Lloyd Webber "opera" about Eva Peron, is living up to its reputation as the Cinderella of British musicals.

The show is sold out through November, and a hopeful queue seeking the occasional returned ticket forms at least three hours before curtain time each night.

But the smash-hit success has proven too much for the star, Elaine Paige, who this week conceded that her frazzled throat could not handle all eight performances a week. The show's producers announced that Paige's understudy, Susannah Fellows, would share her billing and sing the part two times a week.

Paige has been plagued with throat strain from the start. She missed 10 of the first 50 performances and a total of more than a dozen since "Evita" opened in June.

After a week's rest in August, Paige went back to playing all the performances, but finally the effort proved too much for her voice.

Paige's vocal strain is unlikely to slow down the "Evita" juggernaut. A Broadway production of "Evita" is planned some time next year. The London cast album will be released soon. The original double album, with which Rice and Lloyd Webber - following the pattern of their "Jesus Christ Superstar" success - blazed the path for the stage production, has sold 250,000 copies in Britain.

What one ticket agency executive calls "quite enormous," advance sales for "Evita" - no tickets are available until March - are also boosting business at other West End theaters. People attracted to the publicity surrounding "Evita" are booking for other plays when they are unsuccessful in getting tickets to their first choice.

The Cinderella metaphor has adhered to "Evita" from the start. The show's depiction of Eva Peron's life begs for it. The acclaim for "Evita" after the deservedly unhappy record of recent British musicals confirms it.

But the comparison is clinched by the deliberate casting of relatively unknown actresses in the title role. Almost predictably, Fellow's agent greeted her break this week by saying, "For her, it's a bit like Cinderella getting her ticket to the ball."

It was the same for Paige, who won the part after a highly publicized talent search. It was perhaps more of a break for Paige, because of Julie Covington, who sang the role on the original album, had the stage role all but reserved for her.

"She would have been almost certain to have gotten the part in the show if she had wanted it - we would not have bothered to look elsewhere," Rice has said.

Covington, whose clear, ringing voice provided what is still the definitive vocal performance, decided against doing it on stage. She already had refused to promote a single of "Don't Cry For Me, Argentina," the show's most famous song, because she objected to it being released out of context. It made No. 1 on the British charts anyway.

The versatile Covington last month made her operatic debut in the English national opera's production of "Seven Deadly Sins of Ordinary People," the last Brecht-Weill collaboration. At the Stage Door on opening night was Lloyd Webber with an armful of ropes for Covington.

Hers is not a voice to be easily exorcised. But the slight boyish Covington, who usually wears her hair short, probably could not have matched the dramatic verve of Paige, whose blond, more conventional sex appeal assured her of popular acclaim.

Despite its clamorous reception by the British press, "Evita" has not escaped bitter criticism, usually because of its "political" subject matter but sometimes because of what is viewed as the presumption of calling it an "opera."

One of the most scathing criticisms came from Bernard Levin, a columnist and reviewer whose style approximates William Buckley's and whose op-ed columns are as likely to rhapsodize about Wagner or Schubert as to raise the plight of East European dissidents. Levin said "Evita" provided him "with one of the most disagreeable evenings I have ever spent in my life, in or out of the theater."

He excoriated "Evita" as symptomatic of popular culture which, among other sins, "flatters, adding just enough information or novelty to make its prospective purchasers think themselves cleverer than they are."

Of "Evita" in particular, Levin said: "There is a still greater corruption at the heart of this odious artifact, symbolized by the fact that it calls itself an opera, and has been accepted as such by people who have never set foot in an opera house, merely because the cliches between the songs ('Let's Get This Show On the Road' - 'This Crazy Defeatist Talk' - 'What, Commit Political Suicide?') are sung instead of spoken, and the score includes, among the appropriate 'slow tango feel' and similar expressions, such markings as 'poco a poco diminuendo'."

The thrust of most of the criticism, however, is that the show glorifies, however unintentionally, Eva Peron and Peronism. The authors have certainly tried to play down politics, to the point of being criticized in a leftist magazine, "The Leveller," for their "apolitical liberalism" and their creation of "a familiar type in bourgeois mythology - the saint who is also so very 'human.'"

Music critic Derek Jewell, the most effusive supporter of Rice and Lloyd Webber (he is credited with having "discovered" them in 1969) wrote: "Political reaction to the opera in some quarters (depicting evil onstage, etc.) has amazed me and wouldn't have done much for Will Shakespeare either."

But is "Evita" an opera? It certainly sounds less like one on stage than it did on the album. This is no doubt due to Paige's belting, sometimes ragged voice replacing Covington's incisive pitch; to certain reorchestration; and to Hal Prince's staging which - however elegant - is more in the tradition of Broadway musicals than in the more static style of most operas.

But there's no reason to doubt that opera repertory that is elastic enough to admit Gilbert and Sullivan, Brecht and Weill, and Gershwin will someday include "Evita," "Jesus Christ Superstar," and perhaps The Who's "Tommy."

In the meantime, "Evita" will see that, in one of Rice's "cliches," the money keeps rolling in. "Jesus Christ Superstar" is in its sixth year here. Colleen Moore Laughs a Lot Patty McCormack's in the Running