NEW YORK - This is the tale of two actors in drag, enormous bazooms, millions of bucks, and Mr. and Mrs. America.

It’s also the story of how a piece of theater, when it’s very good and in high-talent hands, is mystically flexible.

The first actor is Harvey Fierstein, irrepressible and a master portrayer in drag. Largely - but not completely - on his reputation as a man who could make the outrageous seem plausible, the musical Hairspray was wolfing down sizable advance orders two years ago this week, before it officially opened on Broadway.

About a year after the opening, Fierstein would go on to win his fourth Tony, one of the show’s eight Tonys, for his portrayal of Hairspray’s flamboyant mom, Edna Turnblad.

The second actor is Michael McKean, who had never until now set foot on a Broadway stage. A writer and veteran character actor in movies and on TV and a former Saturday Night Live player, McKean is probably best-known for his role as Lenny in the Laverne & Shirley sitcom and for such films as A Mighty Wind and This Is Spinal Tap.

McKean’s versatility is a given; he and his wife, actress Annette O’Toole (Smallville), were nominated this year for a best-song Oscar, and McKean won a Grammy in February for cowriting the song "A Mighty Wind." In May, his newest role was - Hairspray’s Edna Turnblad.

After more than 700 mega-energy performances, Fierstein donned his fat suit and housedresses a final time, then handed the wardrobe - massive bosom and all - over to McKean.

This sort of Broadway moment happens occasionally, and is pregnant with risk. Was Fierstein Hairspray incarnate, the person who made the show work? Or, like much that is good in life, was he so masterful, so brilliant, that he merely seemed indispensable?

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Millions of dollars hinged on this question. Hairspray takes in about $900,000 a week and has grossed almost $95 million since the first curtain rang up on a chubby life force named Tracy Turnblad, who rousts herself from bed as she sings a buoyant "Good morning, Baltimore!", vows to "eat some breakfast and change the world," then runs off to high school.

She confronts, for two kinetic and riveting acts, her failure to look like a model girl with big hair, the racism of the ’60s that forbids her from dancing with black teenagers, the generation gap, the emergence of television as a force for change, the vacuous nature of power, the vagaries of business theory, and first love.

Mix all these themes in a Broadway blender and what do you get? Essentially, a musical that examines what is right and what is wrong - then plows ahead full-force to do what is right, even if that’s the toughest route.

That sentiment, plus fabulous songs, dancing and a lot of laughs, is why Mr. and Mrs. America flock to the Neil Simon Theatre on 52d Street, and pay as much as $100 a seat.

The theme of the show may be found in the name of its last song, "You Can’t Stop the Beat," and the sensibility of the show in "Cooties," but its heart and soul is in a gospel-like song called "I Know Where I’ve Been." "There’s a road," the lyrics declaim, "that must be traveled."

Through all of Hairspray, Tracy Turnblad’s over-the-top mother, Edna, guides her and goads her and generally provides a steadying influence. This is the Edna who is played in drag.

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Independent filmmaker John Waters, who uses his hometown, Baltimore, as the setting for his stories, made his Hairspray in 1988, when he already was a known and admired quantity. His big leading lady was a man. The girthy Divine - filmdom’s most famous cross-dresser and a genuine American movie curiosity - played Edna.

Hairspray’s Broadway creators turned the film comedy into a musical with Waters’ blessing, and Edna remained a role written for a man in drag. Fierstein seemed the perfect - and once you saw him, the only - person for the role.

His Edna was regal in her everyday pronouncements and concerns. He gave her all the right human qualities. Fierstein could easily have jumped into a muddy river of excess, but instead he spent the entire show teetering at the edge of its banks.

He was never far from wholly believable and, at the same time, he was frightfully strange, in everything from his gravel voice to his oversize gestures.

With the same lines, the same blocking, and the same costumes, McKean is performing a different Edna. He has chosen not to impersonate Fierstein. He has, instead, given her his own character - still over the top, but a bit more of our planet.

His Edna is, as drag moms go, fairly unaffected. She gets along on innate wiles, not a far-out personality. You respected Fierstein’s Edna because she was larger than life and there was no way to ignore her. You respect McKean’s Edna because she understands life. And there is no way to ignore her.

Both Ednas make the same points, as emphatically, in the show. The laughs from the audience, though, seem a bit different. McKean’s Edna is more thoughtful and Fierstein’s was more sensual; that difference alone will make audiences respond in different ways.

Hairspray appears to be doing just as well as ever, filling the house to about 95 percent capacity over the course of a week. Not every show with the same type of mid-run switch has done as well; witness The Producers, whose audience drop-off spurred its own producers to bring stars Nathan Lane and Matthew Broderick back to the roles they originated.

One of many fascinating elements of a good piece of theater is the way it bends, the manner in which fine scriptwriting invites interpretation and reinterpretation because well-drawn characters in compelling situations have so many facets. From night to night, even with the same cast, a play can be different, just as each audience is different.

There’s a sort of mystery in it. The very same work is constantly filtered through ever-changing humans, and as the action unfolds, one character may find a tiny new angle or a dynamic never obvious on any other night. The production then takes a slight new shift. It’s like dropping a pebble in the onstage water; the ripple changes the entire surface.

No doubt, these may be subtle variations, and it’s likely you’ll walk into a show six months after you saw it the first time and not notice much change, or even any. But when a new main actor comes along, the entire balance can shift, and with the right talent and direction, the play will still work.

This is why the road show of The Producers, in Philadelphia this winter, was so good - without Lane or Broderick. It’s why Christopher Plummer’s recent King Lear was celebrated for his portrayal, why Gypsy can work well in community theaters even though Ethel Merman is there only in spirit. It is why the four actresses currently giving sterling portrayals of 11 main characters in People’s Light & Theatre Company’s new String of Pearls will continue to explore their personas throughout the run.

It’s why in August 2005, when Hairspray begins its road-show tour at the Merriam Theater in Center City, we will have yet another Edna giving his very own reading of the same script. She will not be Fierstein or McKean. But if the stars align, along with the cast and the director, it will be another Hairspray that grabs you with an extra-firm hold.