YOU have all these stars – Alan Cumming, Cyndi Lauper, Jim Dale, Ana Gasteyer – and a classic Bertolt Brecht play with incredible music by Kurt Weill.

So you’d think Roundabout Theatre’s production of “The Threepenny Opera,” which opened last night at Studio 54, would be absolutely foolproof. Well, not quite.

Director Scott Elliott obviously decided to go for broke in making the production as authentically Brechtian as he could, even having Wallace Shawn prepare a new and gritty version of the original German text by Brecht and Elizabeth Hauptmann.

But authentic is as authentic does, and in “The Threepenny Opera,” authenticity can come at an awesome price: a touch of boredom.

Mind you, just a touch. Weill’s music, the most insidiously seductive sounds the 20th century ever heard, would carry the recitation of real estate ads, especially if read by Dale, who can entrance millions by reading “Harry Potter.”

Brecht, alas, hasn’t weathered the years as well. His theories of alienation – making sure the audience is constantly aware that it is watching theater – no longer fascinate, while his Marxian politics now sound appallingly simplistic.

As Lotte Lenya, Weill’s wife and inimitable interpreter, later put it, Weill himself tired of “setting the Communist manifesto to music.” It was a point well made.

It was the great Lenya who starred in the original 1928 Berlin production, and it was Lenya again who played Jenny (this time round it’s an adorably blowzy Lauper) in composer Marc Blitzstein’s famous off-Broadway adaptation in 1954.

This time it’s certainly a plus that the original Weill orchestrations are used (although Blitzstein’s were pretty faithful) and we have more of the music than in any other New York production.

And unfortunately, much more of the Brecht, which Shawn has vividly adapted in an intellectually justifiable attempt to translate the 1928/1954 shock value to 2006, with a sexual explicitness and scatological frankness that far outdistances the original.

Elliott has also applied his own individual concept of Brechtian acting on his unfortunate cast.

Some survive better than others. Cumming’s gangster-pimp Mack the Knife, probably the original anti-hero, has a sardonic grace, a Scots accent that for the first time makes sense of the “Mac” in Macheath, and a singing voice that is fair enough except when Elliott prevails upon him, against Weill’s express intentions, to shout.

In a misguided attempt to add a special “Brechtian” touch, Elliott has cast Lucy, one of the two warring ladies fighting over Mack, as a man in drag – exposing his never particularly secret virility presumably for shock value.

Brecht, something of a puritan, would doubtless have told Elliott to wash his mouth out, but the actor in question, Brian Charles Rooney, does very well in the circumstances, offering a performance the late Charles Ludlam might have applauded.

As Polly Peachum – the other lady in quest of Mack – Nellie McKay is charming in a gaga fashion, but is permitted to perform as if she were auditioning for “The Sound of Music.”

Which brings us to the three possible reasons to see this weirdly misconceived production: Lauper as the forlorn whore Jenny, and Dale and Gasteyer as Mr. and Mrs. Peachum, Polly’s parents – the criminal masterminds of Brecht’s Victorian London.

Lauper, who gets to sing the opening number “Mack the Knife,” which is normally given to a character simply called The Ballad Singer, seems perfect in this sleazy milieu and sings with a plaintive, Piaf-like chirpiness.

Gasteyer acts in a rigid style, presumably on instruction, but belts out her big number, “The Ballad of the Overwhelming Power of Sex,” with undaunted vigor.

But the performance of the night – and surely one of the performances of the season – is 70-year-old Jim Dale as Mr. Peachum.

Drawing upon his six years of ballet training, his beginnings in English vaudeville, his years with Britain’s National Theatre, and his even more years as a Broadway star, Dale, nimble, graceful, vulgar and funny, shows the world – and probably even the misguided Elliott – just what “The Threepenny Opera” is all about.

Perhaps he should just do it as a solo act.

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THE THREEPENNY OPERA

[**] (Two stars)

Studio 54, 254 W. 54th St. between Eighth Avenue and Broadway; (212) 239-6200.