How do you solve a problem like Francesca, the seemingly virtuous woman who embarks on a torrid affair with a traveling photographer in The Bridges of Madison County? How do you maintain sympathy for an adulterous Italian war bride who finds herself in an Iowa farmhouse in 1965 with a well-meaning former G.I. and two teenage kids?
If you're a movie studio, you cast Meryl Streep and let her work her magic. If you're a Broadway producer turning Robert James Waller's best-selling novel into a stage musical, you hire the honey-voiced Kelli O'Hara, who has a credible Italian accent, a feet-on-the-ground maturity, and hints of the footloose ingenue she was playing on stage only a few years ago. Happily, she's well paired with Steven Pasquale as Robert Kincaid, the ruggedly handsome National Geographic shutterbug who sweeps into Francesca's life - and into her bed with the alacrity of a Harlequin hero. Yes, Pasquale may seem too young for the role, certainly compared to the movie version played by Clint Eastwood. But there's a natural chemistry between the two stars that doesn't smolder so much as simmer, like the vegetable soup Francesca makes for their first supper together.
It helps that Jason Robert Brown (Parade, The Last Five Years) has written a lush and deeply romantic score, filled with rich and melodic duets that show off its leads' terrific voices — their second act rafter-shaker ''One Second & a Million Miles'' is destined to become a cabaret staple. The tunes help compensate for Marsha Norman's more problematic book, which stumbles whenever the spotlight isn't on Francesca and Robert. The story has no real villains, or even antagonists, to work up a plot worth sustaining for 2 hours and 45 minutes. Not Francesca's husband, Bud, played by Hunter Foster as a hard-working, basically decent guy who seems to merely lack Robert's worldliness and wanderlust. Nor their kids (Caitlin Kinnunen and Derek Klena), who make little impression Klena bizarrely morphs from joint-smoking teenage rebel to med school graduate in the blink of a flash forward. Not Robert's ex-wife (Whitney Bashor), who gets a lovely Joni Mitchell-ish song that neither explains Robert's attraction to Francesca nor foreshadows how their story will end. Even Francesca's Iowa neighbors seem more like a ghostly presence; though they move set pieces onto the stage and sit on the sidelines during scenes in an Our Town-ish evocation of a small farm community's prying eyes, they never directly confront Francesca about her affair. That said, Cass Morgan proves a scene-swiper as the binoculars-wielding neighbor Marge, making the most of her memorable solo of longing, ''Get Closer.''
Director Bartlett Sher does his best to fill the space in the Gerald Schoenfeld Theatre. Ultimately, this is a chamber musical that is both introspective and modest at its core. But when O'Hara lets her guard down and opens herself up to the possibility of romance, and when her magnificent soprano belts out Brown's swooping melodies, even a small space can seem as wide and expansive as an Iowa cornfield. B+(Tickets: Telecharge.com or 800-432-7250)