It doesn’t take much to see that Roman Polanski’s “The Ghost Writer” is the smartest English language movie that has opened here in months (and I include in that “The Last Station,” a film that wobbles with a sitcom Leo Tolstoy for its opening half-hour.) As far as I’m concerned, it’s the smartest movie in town right now.

This is the thriller that Polanski was putting finishing editing touches on last year while under Swiss house arrest for the rape decades ago of an underage girl in the United States.

The Ghost Writer

Three and a half stars (out of four)

Ewan McGregor, Pierce Brosnan, Olivia Williams, Kim Cattrall and Tom Wilkinson

star in Roman Polanski's much-acclaimed thriller about a ghost writer who gets in

way over his head doing the memoir of an ex-British Prime Minister.

Rated PG-13 for language and very brief sexuality; opening Friday in area theaters.

Whatever you may think about what Polanski was capable of as one of Hollywood’s long list of self-styled sexual outlaws in the ’70s—not just producers and directors, but stars and music types, too—he was and still is one of the great filmmakers. While that hardly exempts him from the rule of law, it doesn’t exempt anyone else from acknowledging that he is one of the handful of greatest film masters now working.

“The Ghost Writer” is his best latter-day film, the only one to be put in the same company as “Knife in the Water,” “Rosemary’s

Baby,” “Chinatown” and “Tess.” It’s a suspense thriller with crackerjack tension, enthralling wit and no small amount of political chutzpah (more on that later).

It’s about an ex-British prime minister in America writing his memoirs and the new ghostwriter who’s hired when the PM’s first one is found dead on a Cape Cod beach.

The new one is played by Ewan McGregor. The writer has previously had just the kind of success as a ghostwriter that the publisher wants for this memoir that he’s scared is going to be a white elephant of a book no one buys, or reads, or gives a flying fig about. That the publisher is played by Jim Belushi is only one sample of the film’s sublimely and uniformly witty casting.

The ex-PM (Pierce Brosnan) is a virile, highly fictionalized version of Tony Blair, who always seems to find time to talk to his new ghostwriter when the PM’s sweat shirt is soaked from the workout he just finished (typical of the kind of pungent power detail the film is way too smart to underline).

He’s embattled in his own country for rubber-stamping American aggressions and enthusiastically joining the “war on terrorism.”

With the PM’s first ghostwriter now mysteriously dead (and the first draft of his memoir not much livelier), he now has to answer questions from his new one to get something resembling a commercial draft of the manuscript to his publisher in record time.

Even though the PM, his security team and his whole menage (including a wife who doesn’t sleep with him and a secretary who does) are ensconced in a sleek, ultramodern vacation mansion for the sole purpose of completing the book, the feisty independence and curiosity of his new ghostwriter are things he hadn’t quite counted on.

Especially when that new ghostwriter finds a cache of pictures of the PM’s loose Cambridge days in a hidden envelope his predecessor taped under a desk drawer.

What do they mean? And what DID happen to that predecessor after all?

The writer’s search includes sessions with some of the best character actors in movies — Tom Wilkinson as a Harvard intellectual whose CIA connections are merrily trumpeted all over the Internet, the great Eli Wallach (94 when the film was made) as a tough old coot who lives by the beach and knows from a life of experience which way the local currents don’t flow.

McGregor — whose intelligence as an actor can’t be masked, even in dimwit roles— is perfect as the cynical but willing ghostwriter. Brosnan is equally so as the PM, all savoir faire and alpha male reason until pushed far enough to reveal as much of the murderous thug within as possible without being in physical possession of an actual weapon.

Olivia Williams plays the PM’s spurned wife, who finds her way to the writer’s bed (for her own reasons).

And — get this now — Kim Cattrall, of immortal “Sex and the City” slutdom, plays the PM’s secretary, whose control of her boss’ schedule seems to extend to bedtime (though we never actually see that. With Cattrall’s proven ability to leer meaningfully on camera, we don’t have to).

You can’t overstate the canniness and wit of the casting here — a former James Bond to play the macho PM, a former “Sex and the City” bedroom freelancer to play the secretary/ mistress in buttoned-up gray suit.

The film abounds in the art that conceals art. Pay careful attention to the light that you see out the windows in almost every scene — when it’s gray and revealed by a nearly open curtain, when sunlight briefly breaks through a curtain parted only a few inches. Every second of this film you remember that a cinematic master is at work.

And that’s the most interesting subject of all.

To all of those conspiracy theorists and political paranoids who wondered why on earth Los Angeles authorities finally prevailed on the Swiss to arrest a man convicted of a crime 32 years ago (after he had long since set up Swiss residence, among other places), this film will provide the thoroughly convincing answer.

So much so that someone should make a movie about that man.

Let’s just say that this is a first-rate thriller that clearly makes a wicked and clever hash of some powerful political entities — entities that don’t like to be fooled with and have international avenues for reprisal: governments, their leaders, their intelligence apparatuses.

To make such a deliberately provocative thriller while an international fugitive from a 1978 rape conviction is either an act of monumental political chutzpah or equally monumental foolishness.

The result in the realms of higher justice?

As Polanski has long known (and as his new movie’s ending confirms again), it’s best to forget it, Jake.

It’s Chinatown.