When a stage set has nine entrances, several staircases, a cast of actors playing actors , and a script that meshes slapstick with wisecracks, you can count on laughing. You can, at least, count on some good belly laughs with Michael Frayn’s zany sex comedy “Noises Off,” which opened last night and runs through Oct. 30 at Penobscot Theatre in Bangor.

In three acts, the show follows a troupe of hapless — sometimes half-witted — actors from the final dress rehearsal of a show called “Nothing On” through its extended and inevitably disastrous run. The action takes you behind the scenes, behind the set, and into the psycho-chaotic ways of this cast of crazies whose lives follow the footlights.

Director Lisa Tromovitch concedes in the program notes that the production was a major challenge for the theater, but the energy expended by the actors, the stage hands (led by stage manager Jenny Lynn) and set designer Jay H. Skriletz paid off. This is one of the funniest shows the theater has produced in recent seasons.

Frayn’s script, of course, is a gem. Not every actor is cut out for the speed and precision this play demands. And even with this capable cast, much of the British style is lost, not to mention the shaky British accents. Yet the actors pull it off hilariously.

Ruth Miller as the veteran stage star Dottie Otley plays her role with nerve, although she doesn’t always speak clearly. Robert Libbey is a hoot as the jealous leading man, and is well-matched by Shaun Dowd as the overly sensitive supporting actor. The shenanigans of these three are the highlights of the show.

As the endearing drunk Selsden, Chuck Cronin has some priceless moments of confusion. Rebecca Cook fervently plays the diligent, victimized stage manager. And Brent Askari, as the frustrated and rather lascivious director of this whole mess, is entertaining in a style much indebted to Dudley Moore. Tim LeConey as the frazzled stage assistant plays well off the other actors.

Kat Minkevich as a ditzy ingenue and Sharon Zolper as a vigilant supporting actor both tend to overdo their lines and actions, but they, too, have many funny moments.

If you’re looking for laughs, you’ll find them by the score in this successful start to the new season at Penobscot Theatre.

“Noises Off” will be performed 7 p.m. Thursday, 8 p.m. Friday, 8:30 p.m. Saturday and 2 p.m. Sunday through Oct. 30 at Penobscot Theatre. Special performances will be 5 p.m. Oct. 22 and 10 a.m. Oct. 27. Singles night is Oct. 27. For information, call 942-3333.