In “Knocked Up,” the highly anticipated new comedy from Judd Apatow — creator of the much loved but poorly rated sitcoms “Freaks and Geeks” and “Undeclared,” as well as last summer’s surprise critical and box-office hit “The 40 Year-Old Virgin” — Ben Stone (Seth Rogen) and Alison Scott (Katherine Heigl) embody two radically different versions of the American Dream.

Alison’s good looks, unthreatening competence, and patience with the eccentric personalities and customs particular to show business, have placed her on the fast track at the E! Network. Ben is a sweet-tempered, innocuous oaf who has emigrated from Canada with a group of buddies to wallow in video games, beer, pop culture nostalgia, and gross-out gags on a ring of sagging couches in a rundown Los Angeles rental. Ben and the boys’ dedication to self-gratification and conspicuous consumption suggests that they share a case of Peter Pan syndrome so virulent that it’s likely contagious.

Romantic comedy logic naturally places these two likable opposites on a collision course, and Alison and Ben’s inevitable “meet cute” at a Hollywood nightclub leads to a one-night stand. But in the cold light of the following day, without alcohol in the mix, the personal chemistry that brought them together has vanished. Biological chemistry, however, is another story.

“Comedy,” according to Carol Burnett and Woody Allen, “equals tragedy plus time.” Eight weeks after she and Ben took the morning-after walk of shame back to their respective lives, Alison realizes that she’s pregnant and Ben is the father. The remainder of “Knocked Up” is a shambling, two hour-plus compendium of standard-issue romantic comedy complications involving career, commitment, and impending parenthood ingratiatingly performed by Mr. Rogen and a platoon of actors with sterling stand-up comedy and improv credentials.

Ms. Heigl, star of ABC’s excruciatingly contrived and outrageously popular “Grey’s Anatomy,” does her best, but her small-screen friendly knit-brow reactions to just about everyone and everything grow old quickly. Keeping pace with a group of scene-stealing comic cutthroats like Paul Rudd (as Alison’s profoundly intimacy-challenged brother-in-law Pete) is a tough race to win, and Ms. Heigl remains out of breath and a length behind all the way to the finish line.

The TV, movie, and pop music shout-outs come fast and furious in “Knocked Up.” If a rogue state military scientist were to synchronize a movie projector with body electrodes that shocked political prisoners each time a character in “Knocked Up” made a pop-culture reference, the civilized nations of the world would be justified in rallying behind the H-bomb.

The line between celebrity and reality in the film’s meta-media Los Angeles is more blurred than it is on VH1. E! host Ryan Seacrest and Apatow alumni Steve Carell and James Franco all play themselves. In scenes alongside Ms. Heigl, these stars’ real-life celebrity gravitas adds to the actress’s own, to the point that she seems to be trapped between her scripted character and her tabloid and awards-show persona. Ms. Heigl also inadvertently torpedoes the verisimilitude of Ben’s slacker get-rich-quick scheme to create an Internet database of popular actresses’ nude scenes in movies. But In each of the otherwise awkward and genuine Rrated sex scenes in “Knocked Up”, Ms. Heigl remains discreetly and unrealistically clothed.

Mr. Apatow’s “The 40 Year-Old Virgin” ruthlessly poked fun at the customs and conventions of male bonding and dating. “Knocked Up” takes on both friendship and marriage with an intense, gloves-off acidity. “I buy these nice towels, he whacks off into them, and they’re never soft again,” moans Alison’s sister Debbie (played with precision passive-aggressiveness by Mr. Apatow’s real-life spouse, Leslie Mann) about life with her inconsiderate husband. Needy and self-hating to the brink of emotional paralysis, everyone in the film’s psyche-war of the sexes, from a club bouncer to a TV network “yes woman” (“Saturday Night Live” cast member Kristen Wiig in a brutally funny cameo) is, in the words of Mr. Rudd’s Pete, “just pissed off and tense.”

Coiled underneath the bright veneer of smart comic energy and perfunctorily hopeful character moments lies a vision of contemporary America as bleak as Bergman’s Sweden. The Internet is either a source of masturbatory illusion or a means by which a 9-year-old can pore over graphic murder photos and her mother can fixate on a map of her local registered sex offenders’ homes. Everyone in the film is aware that “Spider-Man 3” is in theaters, but no one seems to know or care that there’s a war in Iraq. A child’s smiling face is the harbinger of a future offering an “inability to enjoy anything” and nothing more.

It’s funny, but it ain’t pretty. And while “Knocked Up” winds up on a pro-family note, one leaves the theater with the sense that the film’s bitterest moments are its most memorable and authentic, and that unfortunately, in most cases, they are funny because they are true.