The touring production of "Oliver!" playing at Wolf Trap through this weekend is a big tease; this non-Equity knockoff of the 1994 London smash is nearly very, very good. The staging, patterned by Graham Gill after Sam Mendes' West End work, has admirable size and fluidity: As the poor orphan of the title gets swept from calamity to calamity, the grand and grubby London streets teem with people who erupt in bright song. And oh, those songs -- to hear the cast lighting into "Consider Yourself" and "It's a Fine Life" is to be convinced that Lionel Bart's 1960 musical is long overdue for a first-class revival in the United States.

But this isn't quite it, and the missing ingredient is charm. The early going is particularly rough: It's appealing, of course, to watch more than half a dozen orphans in sad little workhouse suits singing "Food, Glorious Food" and "Oliver," but between the broad working-class accents and the rollicking orchestrations, an awful lot of witty lyrics get lost.

It's worse, though, when the action is focused squarely on the adult actors. The usually amusing "I Shall Scream," a flirtatious music hall romp between Mr. Bumble and Widow Corney (who run their workhouse with iron fists), isn't much fun at all. Although there is braying and prancing from David L.J. George and Gwen Eyster, there's no give and take, no thrill to the protestations and chase. And when Oliver gets sold to the Sowerberrys, a pair of dour undertakers who sing "That's Your Funeral" -- the least inspired number in the generally sparkling score -- the broad acting makes the scene positively deadly.

Luckily, Andrew Blau comes to the rescue as the Artful Dodger. After Ryan Tutton, respectably spunky and vulnerable as Oliver, tremblingly sings the ballad "Where Is Love," the Dodger recruits the lost boy to Fagin's den of little thieves with "Consider Yourself." The young Blau already has the panache of a seasoned song-and-dance man; he struts across the stage with such jaunty, infectious style that it seems natural for Adrian Vaux's setting to shift and brighten behind him, and for practically the whole city -- or a cast of nearly three dozen, at any rate -- to join in.

Matthew Bourne clearly deserves a lot of the credit; the original musical staging is his, and he has a gift for creating ebullient street parties. (Bourne's choreography for "Get Me to the Church on Time" was a memorable highlight of the Royal National Theatre's "My Fair Lady" a few seasons back.) Three big numbers quickly follow -- Fagin's "You've Got to Pick a Pocket or Two," then "It's a Fine Life" and "I'd Do Anything" from the doomed fun girl Nancy, each sung with a full complement of urchins -- and each is staged with flair and performed with high spirits. For a while, the show absolutely blooms.

But the production flags as it approaches the heart of the story, due mainly to disappointing performances in leading roles. Mark McCracken's Fagin is spindly and distant, and he seems far too young for the part; he plays the old miser without a whisper of grandfatherly enchantment. The offbeat camaraderie of "Be Back Soon" never quite registers, and McCracken's eccentric phrasing during "Reviewing the Situation" makes a hash of the too-cunning logic that repeatedly bites Fagin on the nose.

Renata Renee Wilson fares better as Nancy; she doesn't sparkle with the kids quite as brightly as you'd hope, but she renders the big ballad "As Long as He Needs Me" with dusky power. Unfortunately, Wilson offers no glimmers of what keeps Nancy yoked to the show's villain, Bill Sikes, who's played with a dull glower by Shane R. Tanner. Sikes's lone number, "My Name!," is delivered by Tanner in murmurs and grunts until he bellows along with the turgid chug-chug-chug at the climax; if horror movies had songs, they'd sound like this.

Plum roles, subpar turns: It raises the question of whether Equity actors would have done richer work (a much-feared actors' strike, largely over non-Equity tours, was averted hours before this show opened at Wolf Trap). There is no guarantee, of course; very little in the theater these days causes as much head-scratching as the casting of musicals. But a production as alternately satisfying and unrefined as this leaves you wondering how good it might have been.

Oliver! Book, music and lyrics by Lionel Bart. Directed by Graham Gill. Additional choreography and musical staging adapted by Geoffrey Garratt. Music director/conductor, Dominick Amendum; costumes, Anthony Ward; lighting design, Jenny Kagan. Through Sunday at Wolf Trap's Filene Center, 1551 Trap Rd., Vienna. Call 703-218-6500 or visit www.wolftrap.org.

Andrew Blau, left, as the Artful Dodger (with Ryan Tutton as Oliver), lifts the spirit of the production.