I watched “Transformers: Revenge of the Fallen” this weekend, and one thing really struck me as I took in the initial (and totally gratuitous) shot of Megan Fox in cutoff jean shorts half-straddling a motorcycle: Wow, she’s hot. Throughout the course of the next 150 minutes – really, did a “Transformers” sequel need to be that long? – I found myself observing Ms. Fox’s work wondering if she had what it takes to transform – pun intended – from starlet to star.

By most standards, she’s already a movie star. She has played a lead in two “Transformers” installments, had a supporting role (as a vacant actress, no less) in the Simon Peg comedy “How to Lose Friends & Alienate People” and she recently starred as the title character in the horror flick “Jennifer’s Body.” Moreover, she seems to have a stranglehold on the current #1 ranking as the Hollywood Girl That Guys Want to Bang. But does this really make her a star?

Not in my book. There was no point in the latest “Transformers” installment where Fox couldn’t have been replaced by Elisha Cuthbert, Jessica Biel or some other former (or future) #1 Hollywood Girl That Guys Want to Bang. When I started to type this up, I actually blanked on her name, and had to look it up on IMDB.com. (Ah, yes, Megan Fox.) If nothing else, that makes her a starlet.

Every year or two, there’s a new crop of young’ns vying for the title of “it” girl, and Fox owns it, for now. But it’s a dicey transition from being a hot young thing to developing a long-lasting, viable career in the movie business.

So, does she have what it takes to become a star?

Far be it from me to pretend to be an expert on the matter, but my gut feeling is no. Watching “Revenge of the Fallen,” I determined that Fox has exactly two expressions: 1) seductive (which she no doubt honed on the poor young fellas she grew up with in Florida) and 2) blank. When Michael Bay wants seductive, she can deliver. When he wants sad, frightened or perplexed, she gives him blank.

“All right, Megan. Give me frightened!”

Starlets are disposable in Hollywood. Anyone who is in a film purely as a T&A placeholder can and will be easily replaced. For a starlet to go on to have a long and successful career, she has to possess some combination of the following: 1) serious acting chops, and/or 2) a cuteness that makes her non-threatening to her female audience.

Gwyneth Paltrow is an example of the former. Her big break was in “Se7en” as Brad Pitt’s gorgeous but doomed wife, and she then starred opposite David Schwimmer in “The Pallbearer.” Her career could have faded into nothingness, but the girl proved she could act by taking not-so-easy roles in “Emma” and “Great Expectations,” and winning an Oscar for Best Actress in “Shakespeare In Love.” At that point, we knew that she was always going to be able to find work. The same goes for Julia Roberts, Halle Berry, Nicole Kidman, Charlize Theron, Hilary Swank, Reese Witherspoon, Kate Winslet, Angelina Jolie and Renee Zellweger, who have all been honored by the Academy one way or another.

As for the cuteness factor, there are numerous examples of actresses that are known more for their likability than they are for their acting chops: Meg Ryan, Sandra Bullock, Drew Barrymore, Cameron Diaz, Jennifer Garner, Jennifer Aniston, Kate Hudson and Kirsten Dunst are just a few examples. The aforementioned Oscar faves Zellweger, Witherspoon and Roberts also have an innate cuteness that women seem to love. Of all the romantic comedies that have come out in the past 10-15 years, three out of four have probably starred one (or more) of these actresses.

Unfortunately for Ms. Fox, she doesn’t fall into either category. She currently lacks the acting chops to go serious, and the fact that she’s drop-dead gorgeous actually works against her, as it alienates much of the female audience that so strongly supports the rom-com genre. In comparison to some of her peers, Scarlett Johansson is just as pretty, but proved in “Lost In Translation” and “Vicky Christina Barcelona” (among others) that she is a capable actor. Katherine Heigl is beautiful, but has a built-in fan base from “Grey’s Anatomy” that has allowed her to cultivate a significant career in romantic comedies. Anne Hathaway, Rachel McAdams and Natalie Portman aren’t necessarily on the knockout level of Fox, but they have proven that they can act.

No, Fox’s career seems to be headed the way of Jessica Alba, another former #1 Hollywood Girl That Guys Want to Bang. Alba made a splash on television with “Dark Angel,” starred in “Sin City” and a couple of “Fantastic Four” flicks, but since then it has been nothing but flops like “Into the Blue,” “Good Luck Chuck,” “The Eye,” and “The Love Guru.” Another example would be Jessica Biel, who has starred in “The Texas Chainsaw Massacre,” “Stealth,” “Next” and “I Now Pronounce You Chuck & Larry.” Her career, like Alba’s, appears to be based mainly on her looks and is heading sideways at best.

Jessica Alba: actress.

Fox has a couple of options. First, she could continue to make the kind of movies she has been making. She has yet to reach the same level that Alba has, but she’s getting there. Surely, there are a couple of big action flicks and a few bad comedies down that road. Or she could use her “Transformers” money to find a good acting teacher and work tirelessly on her craft. A couple more installments will keep the cash rolling in. Once her teacher deems her ready, she can find a few smaller roles that won’t allow her to lean on her looks. (Think Jennifer Connelly as a drug addict in “Requiem for a Dream.” I’m convinced that it completely revived her career. Before that, she was known, at least to me, as the well-endowed knockout that rode the mechanical horse in “Career Opportunities.”) But back to Fox – if she goes that route, critics (who were hot for her all along, but loathed themselves for it) will applaud her courage and tenacity. From there, she could very well go on to have a serious acting career.

Does she have what it takes? Not right now.

But damn if she doesn’t look good in a pair of jean shorts.