Decidedly, Olney Theatre is getting considerable comic mileage this summer out of the deep, drawling American South.

With Larry Shue's romp through rural Georgia, "The Foreigner," it had one of its biggest hits in years. Now, it has moved over two states to small-town Mississippi, where a good-hearted tramp named Carnelle Scott is entering "The Miss Firecracker Contest." Mississippi is, of course, the favored territory of playwright Beth Henley, and while she is not quite the silly-billy that Shue is, her comedy has more than its share of eccentric merriment.

At Olney, it also has two jim-dandy actresses heading the cast -- Marcia Gay Harden, as the would-be beauty queen, who yearns to leave the narrow-minded town "in a crimson blaze of glory"; and Brigid Cleary, as a seamstress named Popeye Jackson, who learned her trade by making little outfits for bullfrogs and is now stitching up Carnelle's official red, white and blue wardrobe. (In keeping with that patriotic motif, Carnelle has also dyed her hair fire-engine red, and for the talent portion of the competition, worked up a tap dance with twirling silver batons to "The Star-Spangled Banner.")

In any other context, Henley's oddball characters would probably qualify as poor white trash. They tend to be loose in the morals department -- indeed, Carnelle's easy ways with the menfolk have already earned her the unofficial title of Miss Hot Tamales. Nor are they the smartest of God's creations. (Popeye is clearly one of the slower thinkers in a society where no one's brain functions particularly fast. Looking to move on, she asks what state "this place name of Elysian Fields" is located in; informed it's fictional, she replies with childlike disappointment, "Shoot. Guess I won't be going there.") Amusingly dotty, they can also be downright mad -- to wit Carnelle's impetuous cousin, Delmount (Tim Choate), whose behavior occasionally matches in unruliness the outlandish Medusa-like curls on his head.

Henley succeeds, however, in endowing them with true poetic luster. It's not just the picturesqueness of their speech or their honeyed accents; they all have rich imaginations, unfettered or at least unchastened by the "normal" ways of perception. The world is stacked against them -- and the Miss Firecracker contest, above all -- but they aren't about to capitulate. There's a gallantry to their misguided perseverance, and a charm to the fact that they really don't see themselves as being all that different from anyone else, just momentarily more entangled in destiny's paper streamers.

"Firecracker" is not so well organized a play as Henley's prize-winning "Crimes of the Heart," and you'll have to cope with some loose ends and potholes. Although Carnelle finishes last in the competition, she nonetheless arrives at a new appreciation of herself. You may wonder exactly why. You may also wonder why the playwright introduces into the proceedings a tubercular, chain-smoking balloon man (Daniel McInerney). Spitting up blood, he is apparently sexually irresistible to women -- among them pretty, petulant Elain (Elizabeth Barfield), Carnelle's other cousin. Elain is fleeing a lousy marriage for the umpteenth time, feeling the "limitations" of being beautiful and sloshing down the booze when Henley more or less abandons her.

What keeps the play on course, or brings it back when it wanders, is the unfailing zest that Carnelle and her nearsighted acolyte Popeye lavish on a worthless competition that is down to five sorry entrants (one of whom is hunched of back; another, yellow of tooth). For them, it might as well be Atlantic City in September, and the contrast between their high-strung excitement and the tawdriness of the event is often hilarious. Director James D. Waring has a grand time, compounding the confusions in Carnelle's dressing room as she battles stage nerves, an ill-fitting costume, a recalcitrant hairpiece and a meddlesome pageant official (Rebecca Koon), who blows the whistle around her neck somewhat the way Joshua sounded his horn.

Harden, a fearless actress, gives herself over entirely to Carnelle, playing her cheap as gum and brassy as a bad dye job. Rehearsing her idiotic talent routine, she is a splay-legged disaster. Rouged and mascaraed for the runway, she is a painted hussy. But Harden never loses sight of the waif who has been "trying so hard to belong all my life . . . I just don't know what you can reasonably hope for in life." That sense of bewilderment infuses the performance with improbable sweetness and softens its hard edges.

Cleary, meanwhile, is playing Popeye's idiosyncrasies to the hilt, spouting her lines in a voice that sounds like Lily Tomlin's Edith Ann with a severe head cold, walking blindly into the walls, squirming in the furniture, examining people and objects at a distance of three inches (and at that, through thick spectacles and a thicker magnifying glass). It's such a colossally entertaining piece of character acting that you hate to complain it sometimes throws the rest of the play out of kilter.

Choate is fine as the cousin, whose pallor is both that of the Romantic poet and the asylum inmate, and Koon neatly suggests that the momentary officiousness of the pageant official is inspired by a lifetime of frustration. Waring's two sets, however, are on the makeshift side. The first-act family house proves bereft of telling detail, while the second-act carnival grounds overlook the poetry in shoddiness. More evocative locales certainly wouldn't hurt. After all, some kind of strange southern magic is at work here. For all their tribulations, Henley's main characters do end up bathed in the glow of exploding fireworks, contentedly proclaiming the rose-colored night "as nice as they come."