“Big Fun” is what a children's librarian I know promises to the kids who join her summer reading club. Yet what does she give them once they turn in the lists of books they've read? Rubber spiders, plastic bracelets, sea-horse combs, free ice cream, connect-the-dots puzzles, paperback books, and magic shows performed by apprentice prestidigitators. It doesn't matter. The kids read diligently, turn in their lists proudly, and revel in their measly rewards. Conviction carries the day. Because she believes in the importance of the program, so do the kids. And Big Fun is had by one and all.

Of course, these same kids know where Really Big Fun is to be had during the summer. At the movies. This summer the designated megahits are Steven Spielberg's Jurassic Park and the John McTiernan-Arnold Schwarzenegger Last Action Hero.

Jurassic Park is all about dinosaurs, and for most kids dinosaurs are the very definition of Big Fun. Spielberg's are wonderful. It's not so much that you take them for real as that you marvel at the deftness of the manufacture. At the end of the movie, the paleontologist-hero played by Sam Neill, having survived several dinosaur attacks, bemusedly gazes at a bird flying past his vehicle. You sense what he's thinking. So this is what's left of the awesome monsters: gentled by evolution into harmless birds. But when I drove away from the theater, it wasn't birds I was rediscovering. Instead, I found myself registering faint waves of unease each time I pulled in or out of the paths of trucks. The noise and power of rigs kept reminding me of what Spielberg had evoked on screen: not the strangeness of ancient animal life but the crushing monstrosity of big machinery. Watching monster vehicles grind each other to smithereens is entertainment for some people. Jurassic Park is a slightly upscale version of those destruction shows.

Did it work for me? Not quite. Oh, I enjoyed myself, and I still think of Spielberg as a gifted entertainer. He is never content to merely photograph the amazing saurian inventions of his engineers but insists on investing his moviemaking with its own delights. He is a master craftsman who knows how to foreshadow, counterpoint, encapsulate, build a crescendo, manage a decrescendo. And so certain moments linger in the mind: the sight of water trembling in a glass just before we hear the footsteps of the tyrannosaurus rex; the screeching of a car's wheels turning over in a rut suddenly answered by the remarkably similar sounds of the king dinosaur's cry; a smaller but equally vicious raptor wavers for a split second in its onslaught on three humans and actually seems to grin as it decides whom to attack first.

And yet this movie sadly confirmed for me the fact that Spielberg is growing more and more careless and even callous in his storytelling. When he isn't wowing us with cliffhanging suspense and unusual images, he is often bungling details of action and characterization. As befits a movie that features both the huge brachiosaurus and the much smaller coelophysis, there are both macro and micro stupidities in this movie.

Macro examples, first. The basic idea of a park filled with huge, infinitely dangerous monsters controlled merely by computers (those neurotic and unreliable machines!) and only partially charged electric fences seems the brainchild of a peculiarly self-destructive crackpot. Yet the entrepreneur of Jurassic Park, as written by Michael Crichton and winsomely played by Richard Attenborough, is meant to be basically sane, feyly charming, wholly benevolent. And it is this jolly old Santa Claus of a capitalist who gleefully allows his beloved grandchildren to be the first tourists in the park even after he's been warned that the more intelligent of the saurians have been testing the fences for nonelectric segments! And why would a millionaire with his pick of the best computer experts in the world hire an obviously sleazy, mercenary, and uncaring slob to cybernate his potentially lethal amusement park? (I've recently learned from readers of Crichton's novel that the book's millionaire is a greedy megalomaniac. Now that makes sense!)

Now, micro examples. If the hero knows that dinosaurs are attracted to movement, why does he bolt from the adequate shelter of a large rock in order to run away in full view? Why do monsters who can't hear the loud chatter of humans hiding in a kitchen with echoing acoustics suddenly hear the drop of a ladle to the floor? Why does the hero, who has just discovered his fatherly instincts while protecting Attenborough's grandchildren, pretend in full view of the kids, who are understandably in a state of near-shock, to touch a live wire and suffer death by electrocution? The moment is meant to be funny but comes across as sadistic. And what has happened to Spielberg's skill at directing children? The young actors here are allowed to bicker so obnoxiously that I finally wanted to see them become saurian snacks. All this demonstrates that Spielberg no longer knows how to put real toads in his imaginary gardens. He is losing the human touch that made the fantasies Close Encounters and E.T. convincing and poignant as well as eye-popping.

None of this makes any difference whatsoever to the thousands of kids who have lined up to see the movie. They have come to see big beasts on the loose making mouthfuls of us little, less interesting beasts. And that is exactly what they get. Jurassic Park is Big Fun all right. But some of it is just Big Stupid Fun.