There’s a moment — only one — where you’re brought up short by the presence of a very real and very good film director at the helm of “Dear John,” the latest sloshy, big box office movie adaptation of a Nicholas Sparks best-selling romance.

DEAR JOHN

Two and a half stars (out of four)

STARRING: Amanda Seyfried, Channing Tatum, Richard Jenkins, Henry Thomas

DIRECTOR: Lasse Hallstrom

RUNNING TIME: 102 minutes

RATING: PG-13 for some sensuality and violence

THE LOWDOWN: Adaptation of Nicholas Sparks romance about a soldier on leave who falls in love.

The director is Lasse Hallstrom, a deeply sympathetic humanist whose films have usually been worth seeing since “My Life as a Dog,” even the ones that are called “Once Around” and not “The Cider House Rules.”

The moment is this: The hunky young hero (played by hunk of the moment Channing Tatum, this year’s Josh Hartnett) is a conflicted career soldier and has been sent home because his father is dying of a stroke. In this movie full of letters in voiceover that go back and forth between inarticulate people who learn how to write what they can never say to each other, the soldier writes his autistic father a letter about his life and what his father has meant to him.

He goes to the hospital and discovers that his father, for reasons never explained, has been evicted from the room he occupied the day before. The bed where this dying man now resides is in the hall, where it is passed regularly by all the traffic on the hospital floor — visitors, doctors, nurses, orderlies.

The scene then goes on with the young man forced to read his deeply personal letter to his father in a goldfish bowl. There’s power there in the underplayed perplexity and indignity of the situation. There’d have been a lot more if Tatum, as the soldier, had been equal to the emotional demands.

“Dear John” is from a Sparks romance about two young people who fall in very picturesque love while suffering from acute sanitation that separates them completely from other members of our species.

Our soldier is a bronzed surfer who may be the only American soldier on film who has never appeared unshaven or sweaty in battle no matter how arduous the situation.

The beautiful and sensitive student back home that he loves is played by Amanda Seyfried (pronounced SIGH-Fred), a tiny actress with huge eyes and big lips whose acting talent has occasionally even backed up her beauty.

I liked the first hour of “Dear John” unabashedly. It’s a sanitized version of developing young love between an inarticulate lummox of a soldier and an idealistic student, but a superb film director like Hallstrom knows when he’s got pretty people to deal with and, as good movie directors always have, makes good use of them.

So the young people meet and have a two-week idyll, all nicely perceived. He returns to his Special Forces buddies, she goes back to school.

You gotta like these kids. They write each other faithfully. Then 9/11 happens. Things get complicated. His military service becomes a different matter entirely. So does her life. She sends him a real Dear John letter.

What happened? It takes the rest of the film to find out, and work itself out. Not very well if you ask me.

But for a while there, I was rooting for these two absurdly photogenic kids clumsily and sweetly and prettily in love, and I think you will too. That’s because a pretty good film director did.