As big, dumb summer “entertainments” go, they don’t get much bigger or much dumber than “Transformers: Revenge of the Fallen.” The briefly amusing mash-up/crunch-up of a couple of summers back has been recycled into an epic two and a half hours of explosions, ponderous cartoon history, veiled racism and inept geography.

Is it the worst movie of the summer? Possibly. Will everybody see it? Probably.

“Revenge of the Fallen” promises more Optimus vs. Megatron, more Ford vs. Chevy (only Ford is AWOL — they didn’t want to play the bad-guy cars this time), more Shia vs. Megan Fox’s cut-off short-shorts.

That last one, by the way — no contest.

“Revenge of the Fallen” means that the robots that supposedly were terminated in “Transformers” have got back their “spark,” led by “The Fallen” (voiced by Tony Todd, of “Candyman”). They have big plans for this planet that they first discovered thousands of years ago. It’s up to Optimus Prime (Peter Cullen’s voice), the Autobots and their human (American) allies to stop them.

Only the government doesn’t trust our beloved Camaros that convert into killer robots. They’re convinced the ’bots are the magnet that draws the evil Decepticons to Earth for their little brawls. The military men just shake their heads at this civilian foolishness.

“We’ve shed blood, sweat and precious metals together!”

Meanwhile, the idiotically named Sam Witwicky (Shia LaBeouf, not touching that one) is off to college, where he’s pursued by alien co-eds and rescued by the comically hot Mikaela (Fox). Sam is connected to these transforming beasties by his past and an imprint on his brain.

As with the last “Transformers” movie, the early scenes work best. LaBeouf does a great motor-mouthed patter as Sam hallucinates visions of alien hieroglyphics and maps, annoying his astronomy professor (Rainn Wilson, funny in his one scene) and frightening his player/entrepreneur roomie (Ramon Rodriguez). At some point, though, the funny patter and goofy-mom (Julie White, fearlessly foolish) moments end and it’s all about the metal on metal as we circle the globe, sink an aircraft carrier and trash a pyramid or two in an effort to fend off human extinction.

Director Michael Bay decided he liked the laughs of the first 40 minutes of the first “Transformers” movie, so he pushed more laughs into this one — parents-eating-hash-brownie jokes, robots-humping-Megan Fox’s leg jokes, robots trash talking, cursing, and generally acting very street. Two of them have gold teeth, profess to be illiterate and speak a version of “jive” that must date back to “Starsky & Hutch.”

But here’s where “2.0” is better than the original. The GM cars are cooler. The effects are sharper, higher-definition. None of that blur of chrome and steel that made the first film’s fights so tedious.

The banter of the early scenes, the slang-savvy rap that LaBeouf and Rodriguez share about “Pretty Bettys” (the opposite of “Ugly Betty”), the way Fox embraces being exploited for her sensuality — all are abandoned for hours of chases and explosions.

Bay couldn’t bear to edit out a single effect or explosion. Even the third-act return of an over-the-top John Turturro as a disgraced government agent looking for redemption can’t help the “Fallen” get up.

TRANSFORMERS: REVENGE OF THE FALLEN

*

Cast: Shia LaBeouf, Megan Fox, John Turturro, Rainn Wilson

Director: Michael Bay

Time: 2 hours, 31 minutes

Rating: PG-13 for intense sequences of intense sci-fi action, violence, language, some crude and sexual material and brief drug material

WHERE: In wide release