ACT’s track record with musicals has been sparse and uninspired. So it’s a particular pleasure to see “Tales of the City” — an extremely rare venture into a full-blown, potentially Broadway-bound, world-premiere musical — turn out very nicely indeed. Lesser results would probably still have given the company a home-turf hit given lingering affection for local scribe Armistead Maupin’s beloved San Francisco-set books. But as is, prospects for a commercial future are promising, especially if the ingratiating show finds a way to maintain buoyancy through a second act that lays on melodrama and sentimentality a bit thick.

The “Tales of the City” books (the first two tapped here) didn’t necessarily seem a natural fit for this form. Originally serialized in local newspapers, they put a witty contemporary spin on cliffhanger soap operatics with a combination of light satirical wit and constant narrative twists that might well have defied musicalization.

But Jeff Whitty’s book and the score by clever alt-rock act Scissor Sisters’ Jake Shears and John Garden mostly translate the books’ playful yet heartfelt flavor with aplomb.

It’s the Bicentennial in 1976, and after five days’ vacation in S.F., corn-fed Midwesterner Mary Ann Singleton (Betsy Wolfe) calls her parents in Ohio to say she’s not coming back. Her wide-eyed enchantment with the City by the Bay at its height of Me Decade hedonism — though the latter takes some getting used to — is abetted when she’s taken into the home of landlady Anna Madrigal (Judy Kaye), a pot-growing Earth Mother who clucks over her tenants like a hen over chicks.

Mona gets Mary Ann a job at her firm as secretary to cantankerous CEO Edgar Halcyon (Richard Poe), whose family is “like the Kennedys of S.F., except without all that basic common decency stuff.”

She’s promptly hit on by the boss’s son-in-law Beauchamp (Andrew Samonsky), a seduction chronicled in the sharp “Bolero.” But that proves only her first disillusionment.

Ninety-minute first act takes a little while to find its feet on Douglas W. Schmidt’s set of snaking S.F.-walkup back staircases.

But Whitty’s sharp book and the pleasantly diverse if infrequently memorable songs (referencing ’70s disco, Top 40 soft rock and “Hair”-like Broadway “rock” as well as mainstream show-tunery) admirably thread a crowded narrative agenda in terms both spoken and sung. Helmer Jason Moore keeps things brisk, fluid and frequently funny, if not particularly stylish (apart from Beaver Bauer’s flashback costumes). Larry Keigwin’s choreography, not always distinctive enough, excels in celebration of upmarket gay snobbery “Homosexual Convalescent Center.”

After intermission, however, progress bogs down a tad as a pileup of less humorous crises (mostly from Maupin’s first sequel tome, “More Tales of the City”) trigger several more conventional, heavy-handed scenes and songs. It all ends in multiple reunions and hugs, reminding us that a chorus of hugs is never a good way to end a musical.

Nonetheless, “Tales of the City” is always diverting and never worse than merely imperfect. In its casting, ACT reached well beyond its usual bounds toward experienced Broadway (or at least Broadway-aspirant) personnel, with winning results. Wolfe’s Mary Ann, especially, is a naif with a heart, a brain and a big voice. A seven-piece pit band sounds larger than life, and amplification for the singers was terrific on press night.

Tales of the City

ACT, San Francisco; 1,035 seats; $127 top

  • Production: An American Conservatory Theater presentation of a musical in two acts with libretto by Jeff Whitty and music and lyrics by Jake Shears and John Garden. Directed by Jason Moore. Choreography, Larry Keigwin.
  • Crew: Set, Douglas W. Schmidt; costumes, Beaver Bauer; lighting, Robert Wierzel; sound, John Shivers; orchestrations, Bruce Coughlin; music supervisor, Carmel Dean; arrangements, Stephen Oremus, Dean; music director-conductor, Cian McCarthy; dramaturg, Michael Paller; casting, David Capartelliotis; assistant director, Travis Greisler. Opened, reviewed May 31, 2011. Running time: 2 HOURS, 55 MIN.
  • Cast: Mona Ramsey - Mary Birdsong <br> Jon Fielding - Josh Breckenridge <br> Norman Neal Williams - Manoel Felciano <br> Mother Mucca - Diane J. Findlay <br> Anna Madrigal - Judy Kaye <br> DeDe Halcyon-Day - Kathleen Elizabeth Monteleone <br> Edgar Halcyon - Richard Poe <br> Connie Bradshaw - Julie Reiber <br> Brian Hawkins - Patrick Lane <br> Beauchamp Day - Andrew Samonsky <br> Michael "Mouse" Tolliver - Wesley Taylor <br> Mary Ann Singleton - Betsy Wolfe With: Keith A. Bearden, Jessica Coker, Kristoffer Cusick, Kimberly Jensen, Alex Hsu, Stuart Marland, Jeff McLean, Pamela Myers, Josh Walden.
  • Music By: