WITH CONTEMPORARY crowd-pleasers like Beyonce Knowles, Cedric the Entertainer and Mos Def cast in critical roles, we can hope that a diverse audience will pay attention to "Cadillac Records," this significant and entertaining musical history lesson: the story of Chess Records.

The Chicago-based concern was one of the most influential American music labels of the 1950s and '60s - the jumping-off point for legends like Muddy Waters (Jeffrey Wright), Howlin' Wolf (Eamonn Walker), Willie Dixon (Cedric the Entertainer), Etta James (Knowles) and Chuck Berry (Mos Def). It's the place where the blues was transformed from a down-home, rural acoustic pursuit to a plugged-in, mainstream, yet still nitty-gritty urban phenomenon that helped spark a revolution in race relations and popular music. Chicago blues really had two babies - and they called them Rhythm & Blues and Rock 'n' Roll.

In compressing a sprawling history to a (nearly) two-hour movie, sacrifices are made. Here, screen writer/director Darnell Martin has opted to eliminate any references to the Polish immigrant brothers Leonard and Phillip Chess' earlier label and reduces Phillip to near-invisibility. Now he's just the face and hands at the recording console, never even identified! And where is Leonard's son Marshall, who also got up to his eyeballs in the operation from a very early age?

We do get a pretty good sense of what made Leonard (sympathetically portrayed by Adrien Brody) such a good operator, with his menschlike combination of brotherly concern and manipulation of the artists - giving each a shiny new Cadillac instead of a royalty check (ergo the movie's name) when they scored a big hit - and greasing the wheels of industry by paying off radio DJs to play Chess records. It was a move he could justify because it overcame radio's racial prejudices, but helped set a pattern of pay-for-play corruption that became all too common.

With all those great talents passing through the South Side Chicago blues clubs and then into the doors of Chess Studios, there isn't much time to dig that deep into any of the personalities. And some prime Chess players are totally ignored in the pic - like Bo Diddley - father of rock 'n' roll's most famous "beat."

There are nods to Waters' humble sharecropping start and charm with the ladies. And a whole lot about the proud, impulsive nature of his right-hand man and spiritual brother, harmonica player Little Walter (Columbus Short), who goaded Waters into becoming a better musician and vied for the affection of Waters'main squeeze (sympathetically played by Gabrielle Union).

Willie Dixon emerges, correctly, as the soft-spoken brains behind the Chess operation, as author of boldly sexual tunes like "Hootchie Coochie Man," "Wang Dang Doodle" and "Spoonful" that sparked kids on both sides of the big pond - most famously the Rolling Stones - to pick up guitars and learn how to play.

But we learn little about Wolf (beyond how his name fit his scary look and competitive nature), or much about Berry beyond the fact that he mashed up country music and the blues to jump-start rock 'n' roll and became its first headline-grabbing "bad boy" - hauled off to jail for sexual misdeeds with a minor.

The emotionally troubled and alcohol-/drug-addicted character of Etta James was a relative late arrival on the Chess scene, and quite a musical change of pace - serving up sophisticated, jazz-tinged ballads like "At Last" after all that gritty, testosterone-fueled guy stuff. Still, with Beyonce in the role (she's also one of the movie's executive producers), James' persona comes to dominate the latter half of the movie, and bring a hint of romance (with - who else? - Leonard Chess) into the whirlwind.

It's cool that almost every actor in the film sings his character's tunes. With Marshall Chess and veteran musician Steve Jordan working behind the scenes, the new productions closely match the original recordings' aura. But it'd be a crime if the "Cadillac Records" soundtrack album (also featuring some songs not in the movie) became the standard on which Chess Records is judged by newcomers to this scene. There's a mother lode of original recordings still worth exploring, chock-full of riches. *

Produced by Andrew Lack and Sofia Sondervan, written and directed by Darnell Martin, original music by Terence Blanchard, distributed by TriStar Pictures.