WILLIAMSTOWN — The corn really is as high as an elephant's eye in Marsha Norman and Jason Robert Brown's rich, ballad-packed new musical, ''The Bridges of Madison County.''
The show, adapted from Robert James Waller's 1992 bestseller, is having a pre-New York run at the Williamstown Theatre Festival.
For half the price of a Broadway ticket and a drive to the Berkshires, you can watch a very promising show in its developing stages.
And as a bonus you can see a luminous actress born to the leading role of an Italian war bride transplanted to the Iowa farm belt.
It's a performance that most Broadway theatergoers will miss, because the part was written for Kelli O'Hara, the ''South Pacific'' star whose pregnancy has caused her to miss the tryout. She's scheduled to return in time for the New York run.
In the meantime Elena Shaddow, her understudy, is carrying the show.
Blessed with a silken mezzo and the dreamy distant gaze of a woman cheated of her youthful artistic longings, she's extraordinary as Francesca, the vivacious country girl who settles for a US serviceman and a life-cycle not so different from the animals on their farm.
''At 21 a girl begins to grasp the world,'' she sings, ''and let the longing go.''
Cue the arrival, 18 years later, of Robert (Steven Pasquale, of ''Rescue Me"), needing directions to the last of the covered bridges he's photographing for National Geographic. With the husband and kids off for four days at the Indiana State Fair, Francesca fans the sparks between them, and they quickly burst into full Brontean flame.
Norman and Brown have made Francesca more assertive than she is in either the novel or the Meryl Streep-Clint Eastwood movie. They rightly capture the story's 1965 era, between nascent feminism and self-actualization at any cost, between Betty Friedan and the Summer of Love.
An inventive, accessible melodist, Brown ("The Last Five Years,'' ''Parade") has composed a bushel of ballads, torch songs, bluesy numbers, even a tango or two. It's enough to fill nearly three hours' worth of show, when two will do. Pruning is what tryouts are for.
Too many of the songs are monologues that stop the show in its tracks. Many are embellished with choral woo-woos, as though we were in a church and not a theater. The bombast gilds the lily, making Norman's crisp book scenes — squabbling siblings, nosy neighbors — stand out too much as comic relief.
Bartlett Sher's generally sleek staging also succumbs to the story's goopy preciosity, bringing the stars so far downstage during the mooniest numbers that they're practically in our laps.
The most serious challenge this talented team faces is one the novel never met: We never see how the affair transformed these lovers, helped them transcend regret. And since regret defines them from the outset, the ending is a letdown.
Still, ''Bridges'' reverberates with at least half a dozen gorgeous songs.
Michael Yeargan's suggestive set, lighting by Donald Holder that's as intense as the emotions on display, and just-folks clothes by Catherine Zuber that add a touch of humor all conspire to make the show memorable. I'm eager to see less of it again.