Yea, though NBC walks through the valley of the shadow of death, all hope is not lost. “Smash,” the network’s easily engaging new Monday night drama about the making of a Broadway musical, turns out to be quite the little sunbeam. It has some endearing characters, an instinct for backstage meows and a firm grip on its own sense of camp control, which, if nothing else, sets it apart from Ryan Murphy’s now fully atrocious “Glee.”

Will “Smash” pull NBC back from its inexorable slide? Who knows; who cares. In another time and place, “Smash” would have the assured vibe of a hit. But in this too-smarmy, post-“Rent” place, “Smash” too often swoons from an incurable disease known as the theater bug.

Which makes sense because this is a show made by and for people with a lifelong case of Broadway’s restless leg syndrome. Breaking out into song and dance (with full accompaniment) is just a matter of course here, and whether you think that’s wonderful or not depends entirely on your predisposition for spotlights. “Smash” won’t convert anyone to the lifestyle, but it will intrigue those who are already deep in it.

Then again: “I hate the theater. I really do,” grumbles the moody husband of the show’s lead character, Julia, played by “Will & Grace’s” Debra Messing. She’s a hit Broadway musical writer, but she’s promised her husband and her teen-age son that she will take a year off to focus on adopting a Chinese baby. Then Julia begins having stray thoughts about the myth and meaning of Marilyn Monroe. (Because who doesn’t? Everyone from Norman Mailer to the drag queen down the street has tried to deconstruct Norma Jean.)

Soon enough, Julia and her co-writer, Tom (played by Broadway stage vet Christian Borle), are batting about ideas for a big Marilyn musical. Ooh – there could be a number where Joe DiMaggio, Arthur Miller and JFK all sing about what they look for in a woman!

It’s all too enticing, except for the fact that it’s quite possibly a stink bomb. “A Marilyn musical?” character after character asks with an understandable sneer. One of the neat tricks in the first four episodes is how quickly “Smash” converts a viewer to the concept of turning Monroe’s rise to stardom into a boisterous, big-budget show. “There’s something about her,” Julia says. “How much she wanted to love and be loved. She glows with it. She reminds me of a saint.”

Sneakily, an opportunistic office assistant (Jaime Cepero) uses his iPhone to upload a video of Julia and Tom’s nascent effort at a Marilyn ballad, setting the online theater world instantly abuzz with possibility. It’s a “Spider-Man”-style disaster waiting to happen – except everyone wants in. Anjelica Huston gives “Smash” a welcome lift with her rich performance as Eileen Rand, a big-time producer going through a nasty divorce. Her husband (also a big producer) has taken away Eileen’s rights to a “My Fair Lady” revival, and so, having repeatedly thrown cocktails in hubby’s face at various Manhattan restaurants, Eileen decides to produce the Marilyn musical on her own – hawking her jewels and a treasured Degas sketch to raise cash.

Against Tom’s objections, Eileen brings in a talented but megalomaniacal British director, Derek Willis (Jack Davenport), who cautiously reminds “Smash’s” characters (and its audience) that it can take five years to get a musical from workshop to Broadway stage. Nevertheless, “Marilyn: The Musical” begins a mad dash to casting calls.

Which brings us to “Smash’s” essential business: Who will play Marilyn? Two candidates emerge: Ensemble veteran Ivy (“Wicked’s” Megan Hilty) and Iowa newcomer Karen (“American Idol’s” Katharine McPhee, runner-up to Taylor Hicks in 2006). Ivy is everyone’s obvious choice – a curvy blonde with pipes as big as her ambition – but Karen has a luminescence and small-town innocence that suggests something more transformative than a Marilyn facsimile. McPhee gives the part (Karen and Marilyn) her all but falls somehow short of convincing.

Unconvincing for the role, you mean, or for the TV show? Both. It’s a nagging question throughout, as one gets the sneaking suspicion that if “Smash” is anything like a hit, then “Marilyn: The Musical” is not far from actuality. Worse things have happened, I suppose, and one of “Smash’s” strongest attributes is its music, with Tony-friendly songs by Marc Shaiman and Scott Wittman (whose credits include “Hairspray: The Musical” and a whole lot else).

“Smash” has weaknesses, to be sure: Messing’s performance makes me think of chenille throws and long naps; the dialogue gets hacky in every episode; the ghost of “The Playboy Club” sends a chill through the chorus-girl dressing room scenes. But “Smash” also has a confidence that speaks to its pedigree: Creator Theresa Rebeck is an accomplished playwright and TV producer/writer; the show’s other producers and writers have a wealth of stage and screen experience. That expertise makes “Smash” feel a little more special, enough so that Broadway junkies won’t be disappointed by the details.

They’ll also be encouraged to suspend their easily suspended disbelief. Isn’t that all a musical ever asks us to do? Forgive the occasional weaknesses in the book and just enjoy the razzmatazz?

“Smash” is a case where not bad is plenty good enough.