Writer F. Scott Fitzgerald once scribbled “there are no second acts in American lives.” He obviously never witnessed the P.R. value of a rehab stint.

In fact, it couldn’t be more fitting that Miss USA – buxom symbol of all things American – is the latest luminary to don the modern version of a hair shirt. The Betty Ford bandwagon is so teeming with naughty stars and politicos these days that they’ll be hot-racking ere long.

I’m not knocking the concept of rehab, or the fact that getting clean has saved thousands of lives, marriages and families. In fact, there should be nothing about rehab in itself that invites cynicism.

Deciding to check in should be a private matter that nonpublicity-seeking mortals – and even celebs like Robin Williams and Keith Urban – make quietly after wrestling with personal demons. Let’s face it: Neither of those guys needs a media makeover.

But in the era of P.R. b.s., rehab seems less about stars cleansing their bodies and minds than detoxing their images.

The amount of publicity surrounding a VIP’s decision to enter rehab is usually in direct proportion to his momentary desperation. And his need to keep reporters at bay.

Exhibit A is former Miss Kentucky, Tara Conner. According to reports, Conner has been cutting a rusty around Gotham as an underage barfly – in New York? No! – and engaging in other unsavory behavior unbecoming of “American royalty,” as the Miss USA peeps describe their charges.

Enter another all-American ritual – the publicity stunt. Self-promoting nanny Donald Trump, owner of the Miss USA franchise, said Conner “got caught up in the whirlwind that is New York” – yes, blame it on Manhattan – but said Tuesday he’d let Conner keep her crown if she agreed to enter rehab.

I’m not sure how many 12-step programs out there can cure underage drinking, especially since Conner is now 21. But that’s not what’s important here.

Maybe the beauty queen genuinely does have a problem. But by playing the rehab trump card – pun intended – Conner gets to play the most envied role in American society: that of unassailable victim engaging in our national pastime of self improvement. Miss USA indeed!

Conner is just the latest in a long list of misbehaving famous folk to rely on the redemptive power of a rehab announcement:

Who can forget disgraced Rep. Mark Foley, he of lascivious text-messages-to-underage-boys fame? The Florida Republican had allegedly hit on male pages and ex-pages for years.

But after news of his misdeeds broke, where did Foley go? Not to Disneyland, but to rehab, where his extended stay just happened to coincide with the elections. You see, demon rum made him do it.

Ditto for Ohio Rep. Bob Ney, who found himself embroiled in Jack Abramoff’s sleazy web of influence peddling. In announcing his rehab stint in September – just before pleading guilty to illegally accepting Abramoff’s goodies – Ney said he wasn’t “making any excuses” and then proceeded to do just that, declaring “a dependence on alcohol has been a problem for me.”

Apparently, so has greed. Wonder if there’s a rehab for avarice?

Then there’s Mel Gibson, whose anti-Semitic and misogynist rant against cops in August threatened to undermine his soon-to-be-released movie; Rep. Patrick Kennedy, who flattened a Capitol Hill barricade with his car in May; and “Inside Edition” anchor Pat O’Brien, whose detox stint happened to coincide with some embarrassing voicemails he allegedly left last year.

Whether they actually needed help – and some surely did – is beside the point: Rehab has become an absolution, a celebrity mulligan, a Get-Out-of-the-Gossip-Pages-Free card.

And P.R. agents – who’ve made rehab the first step of second acts in celebrity lives – can’t complain if fans no longer buy such convenient redemption.