Life on the frayed edge of the American Dream comes vividly and urgently to life in LITTLE MISS SUNSHINE, a new musical by James Lapine and William Finn now finding its feet at the La Jolla Playhouse.

Based closely on the irresistible 2006 film about a game little girl from Albuquerque leading her dysfunctional family to California for one of those creepy pre-pubescent beauty contests, the musical gains considerable depth from Finn’s score, maybe his most satisfying ever. (His best-known work, a trilogy of flaccid art songs distilled into “Falsettos,” a mild Broadway success in 1992, has not aged well.)

Lapine, a frequent collaborator of Finn’s, has set up this book deftly to hold both the songs and their singers without strain, while offering much wry wit. (There’s even a gag about Supreme Court Justice Clarence Thomas.) And Lapine’s staging, or somebody’s, is just clever enough to be fun without becoming tedious.

(The uncertainty rises from last-minute tinkering with the billing, which includes a promotion of Christopher Gattelli from “choreographer” to “musical staging by.” Such details are important since they reflect a shift in responsibilities on the creative staff. Since there’s not a lot of dancing here, the new title may mean Lapine is sharing directorial duties. Whatever. It works just fine. If the show moves on, major changes in staging should be unnecessary.)

So what are these nice Finn songs? Some, like “Same Old, Same Old,” are efficient exposition. Others, like the mildly outrageous “Grandpa’s Advice” and the truly smarmy “Too Much Information,” when a reigning beauty queen previews bulimia and plastic surgery for the little girls, are just fun by showing off. But the best of them really do illuminate the characters singing, like “I Cannot Breath,” in which an uber-frustrated adolescent breaks his long silence, or “How Have I Been,” a showdown between two Proust scholars over a hunky grad student.

My personal favorite is “Something Better Better Happen,” sung, just a bit flat with frustration, by the mother of the clan and reprised as an Act I finale with a ravishing woodwind and strings arrangement by Michael Starobin, who does his usual exquisite work throughout. This is one of those moments which justifies the entire concept of dramatic musical theatre.

Essentially, this is a road-trip show, taking place on Interstate 40 between Albuquerque and Redondo Beach. Thus, an old VW bus is seen in about five different-sized versions, the largest of which breaks open to better show the family life therein. The director(s) handle this trickery with nonchalant whimsy, thanks to the designs of David Korins, who also joined with enlightened lighting designer Ken Billington to evoke the endless vistas of the West, from desert to mountains to ocean, with splendidly matched skies and effortless fluidity.

There are six principals, six all-purpose supporters and four little girl contestants in the cast, and every one of them deserves to be a finalist in this sweaty epic of lower middle class yearnings.

Hunter Foster and Jennifer Laura Thompson play with touching pluck the parents of a family which sure could use a break. He runs inspirational uplift sessions based on the mantra “Refuse to Lose” (words which make a face ugly just pronouncing them) while she grinds out paychecks as a bank teller.

Grandpa, played with infectious brio by the dear old veteran Dick Latessa, keeps getting thrown out of rest homes for excessive raunch; Taylor Trensch scowls fiercely as the sullen son in his 86th day of total silence, reading Nietzsche; and the newcomer is Mom’s brother, in the person of the sadly aesthetic Malcolm Gets, fresh from a suicide try over the boy who left him for another academic exotic.

In this parade of losers, young Miss Georgi James glows like the eternal flame of familyhood, an adorable, unsinkable butterball who has sort of accidentally wins a spot in the finals of the Little Miss California Sunshine pageant, several hundred miles and just a few days away.

Such is her uncontested stature as family treasure that nobody wants her to miss this wretched contest if she really wants in. For assorted reasons, nobody can be left behind. Thus the monumental expedition, which climaxes in a tacky fanfaronade of over-groomed nymphettes which offers costumer designer Jennifer Caprio at last a forum for wretched excess and the excellent supporting cast a chance to discard good taste totally.

The final results, of course, are reserved for the paying customer. Suffice to say that our girl, in her confirmation dress popping the moves taught her by her randy but loving old grandpa, fully justifies the universal adoration she accumulates by the end.

There’s a temptation here to thank Finn and especially Lapine for what they didn’t do. There are opportunities aplenty for bathos and pandering with such ripe material and, indeed, there are such groaners as a little girl asking, “Where is heaven anyway?” as a song cue. But even such a obvious set-up can produce poetry; one of the answers to the question is that heaven is “where people prize what’s weird about you.”

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