Cynicism and sentiment have melded magically in movies by some of the best American directors, from Preston Sturges and Billy Wilder to Alexander Payne.

Jason Reitman mined the same territory in Thank You for Smoking and his smash hit, Juno, and it's pleasing to report that he's taken another rewarding journey down this prickly path in his eagerly awaited new film, Up in the Air.

Boasting one of George Clooney's strongest performances, the film seems like a surefire awards contender, and the buzz will attract a sizable audience, even though some viewers might be startled by the uncompromising finale. The Paramount release arrives later this year.

Reitman and co-writer Sheldon Turner embellish Walter Kirn's acclaimed novel about a man who spends much of his life in the air, traveling around the country to fire people for executives too gutless to do the dirty job themselves. The character is just about as unsavory as the corporate pimp played by Jack Lemmon in Wilder's The Apartment. When a character begins as such a sleazeball, you know there must be a moral transformation lurking somewhere in the last reel. That redemption never quite arrives for Clooney's Ryan Bingham, which is one of the things that makes Air so bracing.

Before the movie plunges into deeper waters, it seduces us with some of the most darkly hilarious moments to grace the screen in years. Clooney's crack comic timing makes the most of Ryan's acrid zingers as he savors a life without the vaguest threat of commitment. Trouble arises when his boss hires a young dynamo, Natalie (Anna Kendrick), who has the idea of cutting costs by instituting a program of firing people over the Internet instead of in person. Ryan sees his footloose lifestyle threatened, but he is forced to take Natalie on a cross-country odyssey to train her in the niceties of delivering bad news deftly. The interplay between the world-weary Ryan and the naive Natalie makes for delicious comedy, and Kendrick plays her role smoothly.

There's also a wonderful performance by Vera Farmiga as Alex, a dynamo who clicks with Ryan because she's also seeking no-strings sex on the run. (Think of me as you with a vagina, Alex tells Ryan helpfully.)

Eventually, Ryan begins to question the assumptions that have ruled his life. His encounters with Alex and Natalie threaten his complacency. We can't help worrying that the film may take a sentimental turn, but miraculously, it never does. A scene in which Ryan returns home for a family wedding and talks a reluctant groom (well played by Danny McBride) into going through with the nuptials is a beautifully modulated sequence that manages to be poignant without ever falling into slop.

Reitman is a rare director with heart as well as sardonic humor, but he always knows when to pull back. There is only one false note -- a montage sequence near the end in which several of the people fired by Ryan burble about their love for their families -- that simply restates the obvious. But if this tiny gaffe reveals a touch of insecurity on Reitman's part, the rest of the film is perfectly controlled.

The entire cast is splendid. A couple of Juno alumni pop up: Jason Bateman is the smarmy boss who makes Ryan look humane, and J.K. Simmons has a single scene that proves just how much a master actor can convey in two or three minutes of screen time. The razor-sharp editing by Dana Glauberman gives the film a breezy momentum even while it's delivering piercing social insights. Holding everything together is Clooney, who bravely exposes the character's ruthlessness while also allowing us to believe in his too-late awakening to the possibilities he's missed. It's rare for a movie to be at once so biting and so moving. If Ryan's future seems bleak, there's something exhilarating about a movie made with such clear-eyed intelligence.