More a sketch than a fully realized portrait, Le Petit Theatre du Vieux Carre’s production of Arthur Miller’s “Death of a Salesman” is a lumbering, intermittently engaging evening of theater, where solid to exceptional performances are ultimately undone by the production’s technical elements.

Directed by Amy Boyce Holtcamp, it is a noble misfire of good intentions undermined by sloppy execution.

For the few not familiar with the play, Miller’s “Salesman” is a Saturday Evening Post cover gone terribly wrong, the American nuclear family hurtling into a ditch.

Considered one of the great dramatic achievements of the first half of the 20th century, Miller’s tale of the mental and financial unraveling of the world of salesman Willy Loman devastated audiences still flush with the victory of World War II.

Furthermore, it solidified its author’s position as one of the pre-eminent dramatists of his time.

But as audiences at Le Petit will discover, it’s a terribly difficult play to do.

Two-plus hours of uninterrupted defeat, despair and humiliation can wear down an audience and infuriate the viewer at the delusions of grandeur held by its central character.

It demands uniformly excellent acting from its cast of more than a dozen, the lightest of directorial touches and crackerjack production values.

The trick is to avoid playing “Salesman’s” descent into darkness too soon to make sure the evening’s conclusion has impact. That is just not the case here.

Hopeless almost to the point of unbearable on the page, Willy Loman’s exhaustive angst is given a further layer of desperation by actor George Sanchez. With an imposing frame and a whip crack of a voice, Sanchez is the right man in the wrong interpretation.

He and Holtcamp create a Loman who is doomed the moment the lights rise. Frenetic and gripped by a terrifying aphasia, Sanchez lurches from present failures to past lies and back again while ferociously ratcheting up the intensity. After a while, the viewer can endure no more.

Still, there are pleasures to be had. Garrett Prejean and Chris Marroy, as the Loman sons Biff and Happy, share a genuinely familial chemistry with Sanchez and Mary Pauley as the long-suffering Linda Loman. Their quartet arguments across the kitchen table are highlights of the performance.

Ron Gural as Willy’s brother Ben pops the color of every scene he enters, dispelling the imposed despondency. And supporting players Kate Kuen, Emily Russell, Andrea Watson, Matt Standley, Joel Derby and Rachel Whitman Groves all sharply define their characters within the period.

If only the technical aspects had matched their efforts, the show might be worthy of recommendation, but it is on that count where this production comes undone.

Part of the show’s unrelenting heaviness is painted on its surface by Diane Baas’ oppressively dark lighting design. The lights seem a gloomy wash, little is sculpted, and it has the effect of flattening both the staging and David Raphel’s physically impressive, but visually plain, set.

And Lindy Bruns’ costumes are the worst I have seen from a major offering in this city in some time. Colors are ill considered, accessories are either missing or misconceived, and, fatally, outfits do not always match character.

And unforgivably on more than one crucial occasion, actors’ clothes simply do not fit.

These failures undermine two performances in particular. Casey Groves and Sam Dudley, as Charley and Bernard respectively, are the productions’ gentle grace notes as the father and son that Willy achingly envies.

However, their lovely empathetic turns are almost lost in atrocious costuming.

Preparing to argue in front of the Supreme Court, Bernard is presented in an inappropriate burgundy/rust-colored suit that is too short for his frame, and even worse, Charley’s final scenes have him draped in what can only be described as a double-breasted blanket.

Only the radiant decency of both actors prevents them from being swallowed by these sartorial misfires.

Perhaps a strong producer, invisible but omnipresent, could have caught the missing details that undermine the efforts of the talent on the stage.

Like Loman himself, this “Salesman” has little room to maneuver, and its success requires attention to be paid.

It wasn’t.