Like mismatched roommates, charm and mawkishness are forced into uncomfortable proximity in "Stones in His Pockets," Marie Jones's comic celebration of that essential character out of Irish fact and fiction, the underdog.

Onto the agreeably satirical tale of a film crew descending upon a village in the Irish countryside, Jones has grafted the doleful story of a young man who drowns by weighting himself down with rocks.

The weaving of the two largely incompatible threads is the elaborate task that Jones created for herself in the play, which has just settled in for the month in the Kennedy Center's Eisenhower Theater. And while the actors animating the two-man piece, Bronson Pinchot and Tim Ruddy, are witty and inspired chameleons, their effervescent theatricality is not sufficient ballast for some of the sodden, message-laden sequences with which Jones pads her play.

"Stones in His Pockets" is a long-running London hit, born in Belfast, that made a fairly brief appearance two years ago on Broadway. There, the stars of the piece were two unknowns, Conleth Hill and Sean Campion, who were perfect fits as Charlie Conlon and Jake Quinn, the Irish movie extras at the core of the story. Pinchot, a malleable actor best remembered as Balki on the over-adorable TV sitcom "Perfect Strangers," and Ruddy, an Irish actor based in Los Angeles, are not quite at the level of seeming to complete each other's sentences. Pinchot, in particular, is less than entirely in his element playing one of the central roles, that of an aimless young Irishman with Hollywood pipe dreams.

What's most appealing about "Stones" is the stunt the actors are asked to pull off. In quick-change fashion, they not only play the two extras but 13 other major characters as well, from stuck-up directors to libidinous starlets. They have all gathered in County Kerry, where the film company is making "The Quiet Valley," one of those Celtic romances in which the best acting is done by the scenery. The locals -- including the ancient Mickey, who boasts that he's the last surviving extra from John Ford's '50s epic "The Quiet Man" -- have been corralled into peasant roles, which require them to stand around looking "dispossessed."

Film types are always fun to laugh at (even if they sometimes get the last laugh at the box office). Jones sticks to the tried and true, offering little more than embroidery to the standard-issue figures we've come to know and sneer at: the bullying assistant directors, the muscle-bound security men. Turning movie people into egregious stereotypes almost seems a matter of national honor to Jones; "Stones" is her revenge for all the myths about Ireland and the Irish that Hollywood has perpetuated over the years.

Charlie and Jake are bit players elevated to starring roles, much the way Tom Stoppard promoted two supporting actors of "Hamlet" to marquee parts in "Rosencrantz and Guildenstern Are Dead." They seem to represent what's gone wrong in rural Ireland. Able-bodied but adrift, young but trapped in old, gnawing doubts about themselves, they arrive on "The Quiet Valley" set as two of life's losers. "A nobody" is a characterization that crops up more than once in the play.

They're not merely looking for the 40 quid a day the movie pays, but also for an outlet for the creative energy we suspect they are bursting with. Yet Charlie and Jake hardly feel as if they merit all this attention. Pinchot and Ruddy don't really connect as fellow travelers; their best comic flights are all solos, in which they get to show off in some of the evening's juicier caricatures. On the Eisenhower stage, which is adorned by a trunk, a screen depicting a moody Irish sky, and dozens of pairs of shoes (the legions of other faceless extras) they are able to transform themselves entertainingly into gnarled septuagenarians and ditsy production assistants. (The direction, credited to Hugh Borthwick, seems like a facsimile of the work of the original director, Ian McElhinney.)

Pinchot's best feature has always been his ear; his characters often tend to flower with the addition of a bizarre accent. Here, you can sense his eagerness to shift into voice after showy voice: the solid Scottish bodyguard, the distracted Irish monk, the man-hungry American actress. He proves an excellent physical comic: The come-hither looks he flashes in his exaggerated portrayal of the picture's star, Caroline Giovanni, have classic sketch comedy written all over them.

Ruddy has the advantage of actually being Irish, which gives Jake an authenticity that Pinchot's Charlie never achieves. His Mickey, the old extra, is a model of Celtic crotchetiness: Imagine Walter Brennan on the Cliffs of Moher. And together, the two actors have one delicious moment, a climactic dance sequence that cuts "Riverdance" hilariously down to size.

Still, "Stones in His Pockets" takes a lot of comic capital amassed in Act 1 and squanders it in an increasingly preachy and leaden Act 2, when the story of Sean, a troubled young man from the village where the film is being made, takes hold. Sensitive and misunderstood, Sean throws himself into the deep after an altercation in a pub with Caroline's bodyguard. The incident is inflated to tragic proportions -- Sean is referred to with the hushed reverence of a fragile hero out of Tennessee Williams -- and as a result, satire gives way to sanctimony. "Imagination," a character says, reflecting on Sean's demise, "can be a damned curse in this country."

So can melodrama. "Stones" has its moments, but it's an overlong and overreaching evening. It desperately goes for the gut, when it should have settled for the funny bone.

Stones in His Pockets, by Marie Jones. Directed by Hugh Borthwick. Production designed by Jack Kirwan. Approximately 2 1/2 hours. Through March 2 at Kennedy Center's Eisenhower Theater. Call 202-467-4600 or visit www.kennedy-center.org

Tim Ruddy, left, and Bronson Pinchot play a total of 15 characters.