IF a look at the ocean cools you off in the summertime, you might be curious about ``The Abyss,'' which was filmed about 40 percent underwater. But don't expect a relaxing, warm-weather plunge from this picture. It was written and directed by James Cameron, whose other movies are ``The Terminator'' and ``Aliens,'' and, as you might expect from his record, it isn't stingy with action scenes and violence. Or publicity, for that matter. ``The Abyss'' is the most loudly hyped movie since ``Batman'' flapped into our lives a few weeks ago. Advance word from the studio, Twentieth Century-Fox, told us it would be an adventure with a difference - not just thrills and spills, but complex human relationships, and even a bit of mysticism to get us all thinking. Was the public-relations buzz true? Or would this underwater thriller turn out to be (if you'll pardon the expression) all wet?
I'm sorry to report that ``The Abyss'' is a little on the soggy side. It's big and fast-moving, and it has plenty of energy. But the plot is silly, and for a picture that claims to be out of the ordinary, a lot of its scenes look awfully familiar.
The story begins when a military submarine has an accident, littering the ocean with nuclear warheads. Who's going to clean up this radioactive mess? The workers on an underwater oil rig - who aren't crazy about the job, but have no choice, especially when a Navy crew arrives to supervise the operation.
The big subplot involves the oil rig's boss and his engineer wife, who's in the middle of divorcing him. To top things off, one of the Navy men is well on the way to insanity. This becomes quite interesting when he gets his hands on a nuclear bomb and decides to become a one-man army.
Where does the mysticism come in? Well, every now and then a character sees something that looks like an underwater UFO, and at one point an alien - a kind of snake made out of water - slithers in for a visit.
At the climax, our hero finds himself all alone 25,000 feet under the sea, and there he runs into a whole alien headquarters, where folks are happy to lend him a helping hand. Or fin, or pod, or whatever you want to call it.
The trouble is: This isn't very original. The first 90 minutes are full of ideas that were new in pictures like ``Alien'' several years ago: The settings are messy and lived-in, and many of the characters are rough-and-ready workers who don't look anything like movie heroes. But this isn't exactly startling nowadays.
In the last 45 minutes, the picture tries to be more exotic than ever, but strangely enough it gets even more hackneyed. Most of the aliens look like Steven Spielberg puppets, and the climax is lifted right out of ``2001: A Space Odyssey,'' which has never been pilfered so eagerly in the 21 years since its premi`ere.
``The Abyss'' is expensively made and action-packed, and if that's all you're looking for this summer, it'll entertain you well enough.
A nod of appreciation also goes to Ed Harris and Mary Elizabeth Mastrantonio, whose solid performances keep the movie on a reasonably even keel - dramatically speaking - even when other performers (including Michael Biehn, who overacts like crazy as the villain) threaten to sink it.
If you want an adventure that's really surprising, though, you'd better head for another theater. ``The Abyss'' isn't abysmal, but it's a replay of hits we've already seen - a recycled ``close encounters of the wet kind'' with far too few ideas of its own.