“Oh What a Beautiful Morning.” “All That Jazz.” “Omigod You Guys”?

When the curtains went up in 1943 on “Oklahoma!” and 1975 on “Chicago,” the first two songs plunged Broadway audiences into worlds of defiant optimism and defiant flippancy, respectively. The third, lesser-known entry, the riotous opening to “Legally Blonde: The Musical,” is just as immersive. A Day-Glo explosion of hip-swiveling sorority girls and faux-MySpace lingo (“I’m, like, gonna cry / I got tears coming out of my nose”), “Omigod You Guys” instantly conjures a world best described as flippantly optimistic — perfect for the defiantly undefiant confection that follows.

Last year’s “The Wedding Singer,” also based on a well-crafted but disposable Hollywood comedy, had a similarly dynamite opening number — and quickly went downhill from there. “Legally Blonde” largely avoids that fate; even when Jerry Mitchell’s direction goes the easy route, it packages toe-tapping melodies (by the husband-and-wife songwriting team Laurence O’Keefe and Nell Benjamin) and tried-and-true uplift with a pleasing sheen of professionalism. To quote from the show’s intended demographic, its not gr8 but itll make you LOL. IMHO, obvs.

That target audience, the youngsters who worship the girl-power sturm und drang of “Wicked,” have been asked to shift their sympathies from the green outsider to the perky golden child. As anyone who’s seen the 2001 film knows — and Heather Hach’s crisp book follows the film almost to the letter — Elle Woods (Laura Bell Bundy) is a walking Barbie doll who follows her high-achieving ex-boyfriend to Harvard Law School from their undergraduate days at UCLA. But snooty Cambridge, Mass., filled with people “who wear black even when nobody’s dead,” proves far chillier to her chipper demeanor and heavily accessorized wardrobe (complete with Chihuahua). It takes a high-profile murder trial and a sympathetic manicurist named Paulette (the formidable Orfeh) to make Elle’s perpetually underestimated verve palatable to the smug Ivy Leaguers.

Elle’s sorority sisters surface throughout as a Greek chorus (get it?), although their contributions to Elle’s thought process are less obvious than their intended appeal to what used to be called the tired-businessman contingent of the audience. Nearly a half-dozen dance sequences draw upon Mr. Mitchell’s experience choreographing “The Full Monty” and the annual “Broadway Bares” benefits; among the hardbodies on frequent display is an exercise mogul (Nikki Snelson) with something close to a 16-pack stomach. As clever and eye-catching as Gregg Barnes’s costumes are, I hope he wasn’t paid by the yard.

When he isn’t trotting out the eye candy, Mr. Mitchell — making his directorial debut — shows how much he’s learned from his frequent collaborator, the wizardly Jack O’Brien, most recently of “The Coast of Utopia.” The backup vocalists who pop out unexpectedly mid-song; the throwaway visual gags; the brash David Rockwell sets, including a curving sorority staircase right out of “Dirty Rotten Scoundrels” — Mr. O’Brien’s fingerprints are all over “Legally Blonde,” which is hardly a bad thing.

One lesson still unlearned is that the pivotal moments of a scene needn’t happen as far downstage or as dead center as possible, a ploy Mr. Mitchell uses repeatedly. His several dance sequences, meanwhile, are vigorous but often peripheral to the plot, and a marching-band extravaganza is a direct lift from Gwen Stefani’s “Hollaback Girl” video. But he choreographs with an eye toward his individual characters; from the Delta Nu gals to the lawyers to the tweedy academics, everyone moves in character-appropriate ways.

The movie wouldn’t have worked without Reese Witherspoon’s blend of gumption and naïveté, and Ms. Bundy fills her pink Manolos admirably. Ms. Bundy was Kristin Chenoweth’s standby in “Wicked,” and if she doesn’t quite have Ms. Chenoweth’s rafters-rattling vocal gifts, she gives Elle a far more plausible grounding in reality. She never backs away from or apologizes for Elle’s allure, but her refusal to be defined by it scuttles any impulse to join the Harvard snobs in dismissing her. It’s a sparkling performance, the sort whose strengths may become clearer only in Ms. Bundy’s absence.

Except for a slight boost to the role of Elle’s nice-guy mentor, Emmett (Christian Borle, effortlessly making the segue from character actor to semi-leading man), Ms. Hach wisely opts not to fix what wasn’t broken in the film, right down to the “shocking” courtroom plot twists. Only near the end, when Mr. Mitchell’s interest in the plot appears to waver, does “Legally Blonde” drift into lengthy tangents. Some of these, such as a ridiculous dance break led by Orfeh and the delightful Andy Karl (as her paramour, a UPS delivery man), are more inspired than others, among them a protracted song about “gaydar” that isn’t quite funny enough to offset its tastelessness.

That sequence doesn’t show Mr. O’Keefe or Ms. Benjamin at their finest, but several other songs blend tart lyrics with pleasing, radio-friendly melodies. Michael Rupert has an enjoyable solo as a ruthless law professor, and there’s that opening number, of course. A ballad for Ms. Bundy and Mr. Borle called “Legally Blonde,” meanwhile, is so pretty that the incredibly awkward shoehorning of the show’s title into the lyric can almost be overlooked. And when’s the last time you saw a remix — not a reprise, but an actual dance remix — in the middle of a Broadway musical?

That last fact may prove to be a litmus test in how likely you’ll be to succumb to the peppy, well-scrubbed charms of “Legally Blonde: The Musical.” I, for one, found myself begrudgingly but firmly siding with Elle’s breathless summation: “Like senior year … but funner.” Did I just write approvingly about the word “funner”? Omigod.

Open run (1564 Broadway, between 46th and 47th streets, 212-307-4100).