“Children of Men” may often feel like an ambiguous chase dream, but with Clive Owen leading the charge to save mankind, it’s sometimes hard to see this as a problem.

Loosely based on the sci-fi thriller by P.D. James, “Children of Men” depicts a dystopian society in the year 2027, when the human race has lost the ability to procreate. Caught between an extremist government and increasing violence surrounding the growing immigrant population, Mr. Owen must escort the first pregnant woman in almost 20 years to safety if there is any hope for mankind.

Director Alfonso Cuarón’s tale of the birth of a savior for mankind opens Christmas Day, and his determination to use this mildly futuristic setting as a platform to critique the ills of our current society nearly undermines his film. As we devise more and more ways of making babies, the premise seems increasingly unlikely. Even further off-base is the xenophobic notion that with the world’s population rapidly decreasing, immigrants would risk their lives to flock en masse into Britain for the privilege of being locked in cages and chewed on by rabid police dogs. Similarly, it remains to be seen why the prospect of the human race dying off would make everyone stop caring about the environment but hold fast to anti-smoking zealotry.

Despite these lapses, Mr. Cuarón has captured a compelling Orwellian aesthetic and created a suspenseful chase flick led by an actor who could convince Iranian President Mahmoud Ahmadinejad to talk peace.

The raw masculinity that Mr. Owen brings to the screen is sadly lacking in many of today’s leading men. His reliably sturdy presence and self-confident bearing can anchor most any film, and his voice is so distinctively assured that it came close to making up for the cloaking of his deliciously disheveled face for 90% of Spike Lee’s “Inside Man” earlier this year.

Here Mr. Owen plays Theo, a disillusioned activist who has given up hope for the future and submitted to the impending demise of society. He is joined by a coyly rebellious Julianne Moore, who plays his former lover and mother of his lost child, Julian. When Julian kidnaps Theo to ask for help transporting a refugee across state lines, the drunk bureaucrat is unwillingly charged with the task of saving mankind.

Plot plausibility might be an issue in the hands of another man, but Mr. Owen’s Theo is endowed with a resounding strength of character and restless intellect that pounces into action when necessary. Mr. Cuarón wisely keeps his coiled hero off kilter with various obstacles — even putting him in flip-flops for a large part of the action. But when Theo learns that his charge, Kee (played with a defiant fragility by Claire-Hope Ashitey), is pregnant with the first child to be conceived in 19 years, his long dormant compassion comes to the fore. As it becomes clear that fighting factions are more concerned with their own interests than the safety of Kee’s baby, Theo becomes the lone hope for the girl and the future of mankind.

There is a curious joy in watching cinematic projections of future societies, and Mr. Cuarón does not disappoint. Rather than the slick futurism of most sci-fi films, his setting is gritty and mildly decrepit. Future Britain’s ingrained disdain for the environment seems matched only by its fascination with flat screen (and no screen) technology. The omnipresence of streets bursting with barely contained brutality is countered nicely with enclaves of well-defended independence. Theo’s good friend Jasper (played with jovial eccentricity by Michael Caine) keeps a hidden estate in the woods, and a visit to Theo’s diplomat cousin Nigel (Danny Huston at his egocentric best) treats the audience to a glimpse of the world’s masterworks preserved as opulent living room décor.

But Mr. Cuarón is mostly concerned here with the power of hope in a world nearly devoid of it. Overwhelming violence continually threatens to squelch the glimmer of prosperity that a newborn child will offer, but Theo’s persevering ingenuity keeps the promise alive. And though it becomes tedious to watch an endless string of men lose the use of their intellect the moment they pick up firearms (Theo himself never seems to need them), Mr. Cuarón makes some interesting points. Most moving is the somewhat implausible but still striking silence that a baby’s presence causes in the middle of a war zone.

The details and motivations of the story are not always clear, but they often get swept along by the current of the action. As Theo and Kee face increasingly difficult obstacles in their search for sanctuary with the Human Project — a collection of scientists dedicated to curing mankind’s fertility problem — the fragility of their situation makes it easy to ignore the preachy tendencies of the subtext. And though the architecture of the plot sometimes shifts like quicksand, Theo’s quest, once set in motion, warrants rapt attention.

mkeane@nysun.com