The story of a Coast Guard rescue swimmer who teaches a new generation to brave the wind-whipped seas, "The Guardian" finds Kevin Costner taking the risk of a lifetime.

I'm speaking, of course, about his return to the ocean after the career-swamping disaster that was "Waterworld."

Fortunately, director Andrew Davis ("The Fugitive") makes sure that even when the star dons his wet suit, he's on pretty steady ground.

Costner's Ben Randall is a cranky Coast Guard legend who recently lost his best friend in a disastrous storm and is facing divorce from his fed-up wife (Sela Ward). Unable to handle another rescue, he agrees to spend a semester inland, working with recruits.

The most promising student, unsubtly named Jake Fischer (Ashton Kutcher), doesn't see what he can possibly learn from an old man like Randall. And Randall is hardly thrilled about wasting his time with this cocky kid. If only there were an emergency that might unite them ...

A slightly soggy cross between "Top Gun" and "An Officer and a Gentleman," "The Guardian" is at its best when its heroes race furiously toward their missions, most of which involve jumping out of a helicopter into surging waves.

While Costner characteristically expends minimum energy, Kutcher works almost touchingly hard to prove himself, though he has an easier time with some tasks (brashly seducing teacher Melissa Sagemiller) than others (emotionally confessing dark, dramatic secrets).

Just when things ought to be wrapping up, Davis throws out three different endings, which stretch the running time to a numbing 135 minutes. He should have dumped the heavy themes overboard; a popcorn flick like this does best when it sticks to shallow waters.