What Broadway likes best, Broadway has finally got--a new musical and some stars. No matter that the musical, "Big River," is something less than a certifiable smash. Or that the stars, the very certifiable Rex Harrison and Claudette Colbert, are appering ina piece of 1920s piffle, "Aren't We All?"

All season long, the theater district has resembled a half-empty store, where shoppers have been largely obliged to pick over the same old stock. Most of the new goods were whisked off the shelves as soon as they were put out. Those that weren't have survived largely by the grace of cut-rate ticket plans -- Broadway's equivalent of the fire sale.

Neither "Big River" nor "Aren't We All?" will save the store, but they ought to bring in some browsers. And at the end of what is widely acknowledged to be Broadway's paltriest season ever, browsers are a welcome sight.

Frederick Lonsdale's "Aren't We All?" (at the Brooks Atkinson Theatre) is really no more than handsome window-dressing, one of those increasingly rare instances in the theater when style, of which there is an abundance, triumphs over substance, of which there is none. Lonsdale's drawing room comedies -- gentle explorations of the foibles of the British upper classes -- belong to a vanished world of white-gloved butlers and masked balls. Any plot that has an indignant wife catching her tuxedoed husband in an extracurricular embrace and then goes on to reveal that she, too, has been doing some kissing on the sidelines, is virtually daring us to deny the passage of time.

If audiences are willing, indeed eager, to comply, it is because Colbert and Harrison themselves seem to have magically arrested the hands of the clock. Reference books say that the radiant Colbert is 81, which is enough to shake your faith in reference books. Harrison at 77 seems to be just coming out of the whippersnapper stage, or maybe entering it again. To see them side-by-side on a sofa, engaging ever so subtly, ever so charmingly, in outright flirtation, is to believe in eternal youth.

Actually, Colbert is doing the flirting and Harrison is doing the resisting, and their give and take is very much secondary to Lonsdale's plot. Harrison's son (Jeremy Brett) is the one who was caught in flagrante delicto. But while everyone's wondering if and how he'll patch it up with his wife (Lynn Redgrave), there's still plenty of time for the two stars to indulge in dalliance of their own.

In Colbert's lovely head, it is a foregone conclusion that she will land her man, even though he is an incorrigible womanizer. Self-doubt is simply not part of her makeup (it causes needless wrinkles), but neither is the swollen female ego. Her graciousness is a given, and onstage she appears simply to be obeying her own sunny nature. Like any well-bred woman who believes that gossip should be put in its place, she feels compelled to inform Harrison that "we are being talked about." Astonished, he wants to know how that could be. Without batting an eyelash (although she does arch a fine eyebrow), she replies, "Because I've seen to it that we are." The line is delivered as if it were self-evidence itself.

What makes Colbert such a mesmerizing presence, you see, is not the ageless beauty or the rippling musicality of her voice or even the light mockery that she sometimes directs, sweetly, but firmly, at Lonsdale's inferior creatures. It is that forthrightness. She is a phenomenon who refuses to recognize herself as such. The glamor is real, but her attitude toward it is matter-of-fact. She is merely going about the business of being Claudette Colbert, and if we want to make a fuss, well, that's kind of us, but hardly necessary for her equilibrium.

Harrison is seemingly not out to make any conquests, either. In fact, he is so relaxed, so off-handed, in his delivery of Lonsdale's quips and interjections, that you may suspect him of napping between scenes. With age, he has acquired both the paunch and the squint of a sagacious Eastern deity. (The years are doing to him what they did to Noel Coward -- orientalizing his appearance.) The bristling irony of Henry Higgins has mellowed into a wry amusement and a permanent twinkle has affixed itself to his person. He is, in short, lovable.

On the surface, he is making as little as possible of Lonsdale's repartee, but actually he is making the most of it, and the effortless inflections he brings to the part of a flummoxed old walrus are calibrated for maximum effect. "Are you mad?," Redgrave asks him in a fit of pique. "Not certifiably so," he answers, but in the course of the three-word reply, he 1) expresses surprise at the question, 2) entertains the possiblility that yes, maybe he is, and 3) concludes that, no, his eccentricities fall within the bounds of civilization. That's getting a lot out of next to nothing (including a big laugh). Harrison, smiling slyly into his double chins, gives the impression he isn't even trying.

In addition to the stars, "Aren't We All?" has been astutely cast, right down the line. Redgrave, Weight-Watchers svelte, is dandy as the wife who accuses her husband of philandering and then has to eat her own righteousness as proof of her own philandering comes to light. Brett presents a dapper portrait of manly repentence as the husband. And George Rose and Brenda Forbes add the amusingly priggish accents of a vicar and his starchy wife.

It seems to be an unwritten rule of drawing room comedy that the lighter the play, the more opulent the sets, as if the characters needed fine furniture for mooring, not just standing's sake. "Aren't We All?" obliges with a rich, wood-paneled library in Mayfair and the living room of a cheerful country estate, awash in springtime flowers. Everybody dresses to a T, even if it's just for tea. This world, and the triumphantly trivial playwriting it inspired, may be deader than a dodo. But director Clifford Williams isn't letting on for a second, anymore than Harrison and Colbert are bothering with such realities as birth dates.

At the end of evening, as they're going out the French doors, arm in arm, he finally confesses that he is 48. She admits to 22. I have no reason to doubt either of them.

The big river of "Big River" (at the Eugene O'Neill Theatre) is the Mississippi, naturally, and it starts out in the center of the stage as a planked ramp, then snakes its way back into a pristine landscape of misty green foliage until it merges with the broad horizon. Heidi Landesman's beckoning set infuses the stage with all the expansive promise and wonder of 19th-century America. Mark Twain would have approved.

I don't imagine he'd have too many qualms about this musical version of "The Adventures of Huckleberry Finn," either. It could have been so awful -- cute, hyperactive, sanitized. It could have been Disneyland. It could have been "Huck!" Instead, William Hauptman, who conceived the adapation, and Roger Miller, who wrote the music, have remained largely faithful to the letter and spirit of the novel. Although "Big River" never produces waves of visceral excitement, as the great musicals do, it is an intelligent and feeling piece of work that commands admiration.

"Huckleberry Finn" remains one of the great adventure stories -- Everyboy's dream of breaking free from the proprieties of civilization and venturing, unfettered, out into the great unknown. But for all the colorful escapades and narrow escapes that Huck and Jim, the runaway slave, experience on their raft trip south, the story is as much about the awakening of a conscience. Huck has no reason to doubt the prevailing morality that holds a black man no better than a beast of burden. He's fairly certain he will go to Hell if he does.

But from the passing banks -- and sometimes from the muddy waters themselves -- scoundrels and rogues rear their heads, vent their baseness, indulge their rowdy prejudices. It's enough to give a decent boy pause, especially when the stars come out and the deep night and the dark river blend into one (an image that "Big River" recreates beautifully). By the end, Huck comes to acknowledge what he's feeling in his heart: If treating Jim as a brother means going to Hell, he's ready to have them swing open the gates.

That's a grand theme and "Big River" handles it with integrity and decency, eschewing the sentimentality that warms the cockles of so many Broadway musicals. If you put a pair of nubby overalls on a cornstalk, you'd come up with something resembling Daniel H. Jenkins, the show's appealingly unvarnished Huck, who alternately narrates the tale and acts it out. As Jim, Ron Richardson has the strapping looks to match his strapping voice. Both the show and the performer emphasize the strength and pride that Jim maintains even in shackles, which ought to silence those protesters who persist in perceiving demeaning racial overtones in Twain's tale.

When Huck and Jim join together for "Muddy Water" -- Jenkins' reedy postadolescent tones glancing off Richardson's resonant baritone the way shafts of light ricochet off a forest pool -- the musical offers a potent illustration of human fraternity. "Muddy Water" is the rolling anthem in Miller's rewardingly tuneful score, which never sheds its country twang, perhaps, but puts all the sawed fiddles and the plunked banjos to surprisingly varied use. If there's a complaint to register, it's that Miller's numbers beg off too soon. Certainly the fulminations of Huck's drunken father (John Goodman) against the "Guv'ment" are worth a few more choruses, as is Huck's sprightly proclamation of independence, "I, Huckleberry, Me." The lovely "River in the Rain" quits before it has spent half of its enchantments.

The problem is that there are a lot of pages to transfer to the stage, and "Big River" can't afford to dawdle -- not when Tom Sawyer (a tangy John Short) is on hand to propose his intricate solutions to simple dilemmas. The problems only multiply once The Duke and The King (Rene Auberjonois and Bob Gunton) climb on board the raft, their mad heads full of tattered schemes of their own. They make an undeniably robust pair of conmen, mangling Shakespeare here, undercutting Barnum there, robbing rubes in one town and fleecing fatherless daughters in the next. But their antics also contribute to the distinctly episodic nature of the musical.

That may be the built-in stumbling block, when you're turning novels into plays. "Big River" is constantly leaving one situation behind to go on to the next. It never figures out how to gather its virtues all in one place, but strings them out on a line -- or on a river. Director Des McAnuff does all he can to compensate with a staging as fluid as imagination (and today's theater technology) allows. Keeping the raft bobbing near the footlights, he lets the landscape and its people drift by. Even when the show takes time to go ashore, McAnuff manages to conjure up a bewitching atmosphere -- somewhere between dream and nightmare, fine-feathered fiction and tar-and-feathered reality.

Still, we are left with the nagging sensation that the musical has one foot on the stage, while the other is planted in Twain's book. The stance is sometimes awkward, occasionally precarious. All the more remarkable for that, "Big River" succeeds in standing tall. Taller, in fact, than all the other musicals this season, stacked one on top of the other, which is exactly where they belong.