` NEW YORK -- In the eeriest "Sweeney Todd" ever experienced on or off Broadway, Stephen Sondheim's wicked masterwork is performed by the raving inmates of an old-fashioned madhouse.

Newcomers to the 1979 musical thriller may have problems grasping this wonderfully wild production of the horror show about the vengeful crimes committed by a demonic barber and his terribly practical sweetie. But anybody who has previously encountered their gory doings is likely to eat it up.

Arriving yesterday at Broadway's Eugene O'Neill Theatre, British director John Doyle's extraordinary concept reduces the show's entire ensemble to a mere 10 performers who never leave the stage because they also work double duty as the musicians.

What's more, they're all nuts, or rather that's the notion behind Doyle's extreme interpretation: The tale's simple-minded apprentice, Tobias, apparently undergoes some weird kind of act-it-out therapy in an asylum to revisit the ghastliness that drove him mad. So think of it (not too literally) as a sort of "Marat/Sade" meets "Sweeney Todd."

Hugh Wheeler's macabre libretto about Sweeney and Mrs. Lovett and the good reasons why his slashed victims end up in her meat pies is more or less rendered intact. Originally performed by 28 musicians, Sondheim's grand score has been acutely re-orchestrated by Sarah Travis to yield creepy effects, like the skin-prickling union of a wailing accordion and skittering strings.

Designed by Doyle and framed in dusk, the abstract set consists of flooring and a looming back wall of raw planks. At the rear, the racks of a towering curio cabinet are loaded with eccentric bits of bric-a-brac that at times provide visual comment. For example, while Johanna saws at her cello and trills "Green Finch and Linnet Bird," the lighting illuminates a doll stuffed into a gilded cage. Whenever emotions grow volcanic, the chinks between the planks glow with evil.

The actors often depict their characters in a dislocated manner, staring vacantly out front as they talk, sing and fiddle with their instruments. A crude casket propped on sawhorses functions as Sweeney's barber chair. Throats don't spurt when the barber swings his razor; instead, the stage is flooded by red light as somebody pours red liquid from one white enamel pail into another. When they're dead, characters don gore-smeared lab coats over their eclectic 20th century attire.

By all rights, such a bizarre approach should prove fatally distracting, but thus abstracted and compressed to its essence, the musical magically comes across as an extremely intense experience. Of course, one probably needs to have met "Sweeney Todd" before to fully enjoy such a far-out spin on such already audacious material.

Even so, it's obvious that the performers' commitment to this demanding production is superb. His bullet-headed presence more malignant than most Sweeneys, a sonorous Michael Cerveris hardly curries audience sympathy. The ultracasual manner Patti LuPone languidly employs as Mrs. Lovett wittily enhances the pie-maker's eccentricities.

Mark Jacoby's self-absorbed Judge Turpin, Alexander Gemignani's spaced-out Beadle and Manoel Felciano's dazed Tobias somehow seem more human than when their characters are played naturally. Donna Lynne Champlin (Pirelli), Lauren Molina (Johanna), Benjamin Magnusun (Anthony) and Diana DiMarzio (Beggar Woman) are similarly remarkable.

Despite its intimacy, this is anything but a cozy "Sweeney Todd." The icy nature of Doyle's gripping production produces nearly as many goose-bumps as the lurid story and Sondheim's spidery music.