“The Producers” is hardly the worst movie musical ever – the cinematic roadside is littered with too many unworthy competitors – but it might be the most unnecessary one. Everything that’s good about it was already in the original 1968 Mel Brooks film or the rollicking 2001 stage adaptation.

When the new film works, it’s a moderately effective transfer of the latter incarnation, a big-budget version of what you might see on public television. When it doesn’t work – and it doesn’t work many times, in many ways – it’s a mugging, mincing embarrassment, a textbook example of how some things can sing in one medium and squawk in another.

This much can be said: Unlike virtually every director to try his or her hand at musicals lately, director Susan Stroman knows her way around a dance sequence. She has clearly studied her Stanley Donen and Vincente Minnelli, and her comfort level rises to meet the show’s choreographic demands.

But like Brian De Palma, who focuses so much attention on his gorgeous tracking shots that he sometimes forgets about the actors in them, Ms. Stroman gives her stars either no direction or bad direction. This is the first movie adaptation I’ve seen where the actors played bigger, not smaller, with a cam era inches from their face.

By now, everyone probably knows the brilliantly concise premise. Upon realizing that an unprofitable play never has to repay its backers, the amoral Max Bialystock (Nathan Lane) and the moral-but-fading-fast Leo Bloom (Matthew Broderick) decide to sell 25,000% of “a guaranteed-to-close-in-one-night beauty” and go in search of the worst play imaginable.

But even the most deviously laid plans can go awry, and the fruit of their labors – “Springtime for Hitler,” a musical by an unrepentant Nazi named Franz Liebkind (Will Ferrell, one of the only non-holdovers from Broadway) – becomes a runaway smash. How could it go wrong? Well, Ms. Stroman, Mr. Brooks, and co-writer Thomas Meehan find plenty of ways, most crucially in the film’s depiction of Max.

Norman Mailer once explained that every dictator (with the possible exception of Mussolini) has been physically repulsive, and Max Bialystock is as dictatorial as they come. In the original movie, when Max furtively poked his head out of his office after squiring one of his randy-old-lady backers, Mr. Brooks froze the camera on Zero Mostel’s sweatiest, eye-bulgingest, most grotesque face possible. Ms. Stroman apes the camera angle from the hall but makes the moment impish, cute. We’re watching Puck in Falstaff’s clothes.

Chemistry and craft can cover just about anything on stage, where Mr. Lane got away with the gruff-teddy-bear bit, but the energy is all wrong here. All the comic timing in the world – and Mr. Lane has an indecent share of it – can’t make him scarier or older (Mostel and Gene Wilder had a father-son dynamic that’s missing here) or less tame. “Tame” is a word that should never be applied to “The Producers” and especially not to its Max.

While Mr. Lane’s Max isn’t nearly enough, Mr. Broderick’s Leo is far too much. The adenoidal, clenched-shoulders bit was awfully tired by the time he and Mr. Lane opened earlier this year in “The Odd Couple,” and by now it’s just insufferable.

Mr. Broderick still shows charming proficiency with his musical material – his two big numbers are the best Mr. Brooks wrote for the show – but his book scenes amount to an excruciating laundry list of tics and grimaces. Ms. Stroman’s static staging continually leaves him high and dry, with nothing but his blue blanket and his shtick.

On Broadway, Mr. Brooks, Ms. Stroman, and Mr. Meehan improved upon the 1968 film in two crucial ways: They got Franz and the “Springtime” director, Roger DeBris (Gary Beach), more involved, and they created an actual ending. The original movie hurtles at such a breakneck speed that it sort of collapses over the finish line – Bialystock and Bloom blow up the theater, quick courtroom scene, off to jail, THE END.

The musical remedied this with an act of betrayal and subsequent reconciliation; they’re not particularly funny, but they at least give the story an emotional lift. These scenes feel tentative and rudderless on screen, as if Ms. Stroman were lost without having the original film to cull from, and Max’s 11-o’clock number, “Betrayed,” loses nearly all of the impact it had on stage.

I know, I know: It’s unfair to compare one version against the other. Every adaptation deserves to be judged as an entity unto itself, etc. But this is an exception, because Ms. Stroman and Mr. Brooks have worked so hard to replicate their past incarnations without really thinking about the consequences. They’re fighting the last war, and any historian can tell you how that usually ends up.

Both “The Producers” and the recent “Rent” film enjoyed unusual latitude in casting the original performers, and Mr. Beach is even funnier than he was on stage as the swishy director and Hitler fill-in. (“Heil myself!” he shouts, shamelessly ripping off Jack Benny.) Roger Bart, however, suffers from several cuts and is a nonfactor as Carmen Ghia, Roger’s even gayer assistant.

Ms. Stroman also seems to have found room for seemingly anyone who’s even auditioned for “The Producers” – with the notable exception of Cady Huffman, who created the nubile Swedish receptionist Ulla on stage.

Ms. Huffman’s replacement, Uma Thurman, makes Rosario Dawson – the starlet dropped into “Rent” – sound like Maria Callas, but her go-for-broke physicality matches her work in the “Kill Bill” movies and adds a luscious streak of carnality. She essentially turns Ulla from Broadway’s triple threat back into what she was in 1968: a good-time gal with a bigger cup size than IQ, who isn’t about to get cast in any Broadway musical for her singing ability.

Mr. Ferrell clicks into the story’s manic energy with a minimum of fuss, although a tighter leash might also have come in handy here. (And like Ms. Thurman, he looks about 2 feet taller than all of the Broadway performers. What do they feed these Hollywood types?)

William Ivey Long’s costumes straddle the film and stage versions with a crisp, sumptuous sense of style that eludes the rest of the production. And a few new throwaway gags work reasonably well: Addison DeWitt, the fictional drama critic of “All About Eve,” pans one of Max’s shows, and Leo Bloom’s day of rebirth comes on June 16, which James Joyce fans will recognize as Bloomsday.

But nice outfits and a few sly in-jokes are inexcusably slim compensation. If you’re going to make a movie of the Stroman-Brooks-Meehan “Producers,” make a movie of it. Find a way to take Messrs. Lane and Broderick’s still-potent rapport and adapt it to the screen. As Max would say: “Flaunt it!”

In fact, the only time the film takes real advantage of the new medium comes well into the end credits, when Mr. Ferrell pays Teutonic (and very funny) homage to another film theme song. A movie where the first interesting new idea comes at the 130-minute mark? That sounds like a good bet for the producing team of Bialystock & Bloom.