"The Guardian" is in the long and honorable film tradition of old-salt/young pup movies, in which we learn how great the old salt was, and how much he has to teach the young pup, and how the young pup revolts against the old salt until - well, you fill in the rest.

But instead of being just a long cliché, "The Guardian" is very well made, full of tension and occasional wit, and has been cast with just the right actors. This time around, the film is about the Coast Guard, the Rescue Swimmers who have to go out whenever and wherever to save the crews of sinking ships, or stupid sea kayakers, or whomever, and - the crux of the job - when not everyone can be saved, to sometimes decide who to save and who to let die.

The film stars Kevin Costner as the old salt and Ashton Kutcher as the young pup. Costner is aging these days in much the same way Harrison Ford has - he's thicker around the middle, has a roughened, weathered face - and he's not trying to play for romance or sexiness anymore. Kutcher, with his slightly goofy, off-center looks, also doesn't try to act his way into scenes; he just lets them play out.

The story comes in three parts. Part one, Costner is stationed at Kodiak Alaska where we see him do a couple of great rescues in icy storm-tossed seas, as we say, including a moment when he loses his best friend, while Costner's wife, played by Sela Ward, decides to leave him because he's not really married to her but to his job.

Part two, he's assigned to teach new recruits back down in the lower 48, including young Kutcher, former high school swimming champ and still cocky and obnoxious. This is a long middle section, in which Kutcher finds a girl and also grows up. The training itself is hard enough to make you swear off swimming forever, but like the rescue footage it is very well done, and quite believable.

Part three, Kutcher and Costner are back in Kodiak to save more people, and there is of course a predictably tragic event before we get to the end of the film.

But there's nothing wrong with that; "The Guardian" is an exciting entertainment, well directed by Andrew Davis, who's made a number of other action films, including "The Fugitive," and although there's nothing in the film that we haven't seen before in others - the Marines, Navy Seals, Army Rangers or what have you - "The Guardian" still works, still keeps us on the edge of our seats. The special effects of the rescues at sea are amazingly realistic, and it's impossible to tell where the actors leave off and the stunt doubles take over. There's even an occasional funny line or moment to help relieve the tension. All in all, a fine entertainment; you can't always ask for Shakespeare.