'FROM Justin to Kelly," a quickie attempt to wring a few more bucks from last year's "American Idol" finalists, is arguably the most insipid movie released so far this century.

Kelly Clarkson, who won the TV talent competition and stars as a young woman named Kelly, recently defended Twentieth Century Fox's decision to dump this lame cross between "Grease" and "Where the Boys Are" into theaters without advance critics' screenings.

"I can tell you right now that none of the critics are going to like this movie," she told TV Guide. "They're going to tear into it."

Right on the first count Kelly; wrong on the second.

To truly tear into a movie, it first has to engage you, however negatively.

"From Justin to Kelly" is the movie equivalent of general anesthetic; the handful of unwary civilians emerging from yesterday's first show at the Union Square looked like they had just awoken from a very deep sleep.

The only visceral reaction to this innocuous movie is likely to come from teenage boys who have been diverted from "Hulk" by their girlfriends in favor of this innocuous (and sexless) piece of fluff, which was originally scheduled to hit the video shelves in a mere six weeks (Fox backed off after protests from theater owners).

Oh yes, there is a plot to this movie, a squeaky-clean romance between the big-voiced Kelly and Justin Guarini, the big-voiced and big-haired young man whom she beat for the "American Idol" title.

He plays Justin, who travels with his "Pennsylvania Posse" - the scheming Brandon (Greg Siff) and the nerdy Eddie (Brian Dietzen) - to Fort Lauderdale for spring break, where they are promoting a PG-rated whipped-cream bikini contest and a "margarita madness" event where no one drinks, much less gets drunk.

Kelly, meanwhile, is visiting from Texas with her bitchy blond pal Alexa (Katherine Bailess) and nice black pal Kaya (Anika Noni Rose).

Sparks fly as soon as soon as Kelly meets Justin - in the script, anyway, if not on the screen - but jealous Alexa schemes to keep them apart with phony e-mail messages.

Brandon, meanwhile, keeps getting busted by a sexy cop; Eddie keeps failing to connect with an Internet blind date; and Kaya pursues a Hispanic dishwasher. Exciting stuff.

Kelly and Justin take a boat ride around Miami, where they have this immortal exchange:

Kelly: "So, do you bring all the girls out here?

Justin: "No, I mostly come out here to think."

Kelly: "What are you thinking about now?"

Justin: "How happy I am you gave me a second chance!"

This drivel was fabricated by Kim Fuller, who wrote "Spice World" and is the sister of "American Idol" creator Simon Fuller, who takes an executive producing credit on this movie.

The direction is by the notorious Robert Iscove, who made Freddie Prinze Jr. a star (however briefly) in "She's All That" and added insult to injury with "Boys and Girls."

The impassive Justin, however, makes Freddie look like Kevin Spacey by comparison.

Vacuous Kelly isn't much better; the acting and the '70s-style choreography would barely pass muster in a high-school production.

Both the leads are technicaly better singers than, say, Renée Zellweger.

But their 12 bubble-gum ballads are as instantly forgettable as the movie.

Kelly opens it with one called "I Won't Stand in Line."

That probably won't be necessary to see "From Justin to Kelly," which will be available on video in September.

Llumenick@nypost.com