STEVEN SPIELBERG knows how to begin a movie.

For the first half-hour of "War of the Worlds," screenwriters Josh Friedman and David Koepp's updating of H.G. Wells's 1898 science-fiction adventure about Earth under attack by aliens, I was barely able to jot down a note, unwilling as I was to take my eyes off the screen. And it's not as if the film is that good-looking either. Not at first.

For one thing, it doesn't really feel like a "movie." Not a big-budget one starring Tom Cruise anyway. There's a smallness to it, an offhand quality in the way it introduces us to its central characters: New Jersey crane operator Ray Ferrier (Cruise), a divorced screw-up who has agreed to take his kids, Rachel (Dakota Fanning) and Robbie (Justin Chatwin), for the weekend while his ex-wife, Mary Ann (Miranda Otto), goes out of town. Ray is late for the handoff; Mary Ann is angry but used to being let down; the kids are sullen and hungry; and there's no food in the house. Soon, however, the domestic-melodrama quality of the story gives way to a much different, yet no less verite, style of filmmaking, as Ray, Rachel and Robbie's lives are turned, at times quite literally, upside down.

That's when the aliens arrive.

Rearing up without warning from beneath the streets of small-town Jersey, which buckle and break like sugar cookies, the first of the mysterious exterminating machines (or tripods, as they are quickly dubbed) is a sight to behold. And you can't even see it that clearly, what with the dust and smoke and shaky-camera pandemonium swirling all around it. All of which makes it that much more terrifying. What is it? And what does it want? Thirty minutes in, Spielberg's film feels and looks like a documentary about something too awful and too new to even define.

Of course, what it wants is simple. This soon becomes very, very clear, along with the fact that it isn't an "it" but a "them," as Ray and the kids race -- in a stolen car at first and then later on foot, after a harrowing encounter with a crazed and homicidal mob leaves them without wheels -- past dozens of these merciless machines from outer space.

"It's not a war any more than there's a war between men and maggots," says Ogilvy (Tim Robbins). He's the slightly -- okay, seriously -- nutty guy with a gun and a root cellar who offers refuge to our heroes at the film's halfway point. By now, Robbie has gone missing, and Ray and Rachel quickly start to wonder whether they wouldn't have been safer taking their chances outside than agreeing to hole up in a basement with a fruitcake who fancies himself a member of the "resistance."

It's during this sequence that Cruise does some of his best acting. And it comes not when Ray is forced to make a necessary but morally bad decision regarding Ogilvy, but when Rachel asks him to sing her to sleep, and he realizes, with crushing disappointment, that he doesn't know any lullabies.

This is when it becomes clearest that, despite all the special effects and spectacle -- and "War" does become spectacular as the story progresses -- the movie is at heart a tale of a father's love. That keeps it grounded and credible, even at its most epic moments.

I wrote, at the top of this review, that I was scarcely able to take any notes during the film's initial adrenaline blast. That's true, but that doesn't mean that "War of the Worlds" is flawless. From time to time, I was bugged by certain inexplicable, but cinematically convenient, holes in logic: the digital camera and camcorder, for instance, that appear to be working fine despite the electromagnetic pulse that has disabled all other electronic devices, and the fact that Ray's stolen car miraculously emerges completely unscathed from the crash of a jetliner that destroys the house it was parked in front of. Oh, and then there's the scene where we first meet the aliens close up. Tell me if it doesn't remind you, a little too much, of the scene in "Jurassic Park" in which the velociraptors are stalking the kid hiding in the kitchen.

One last thing. As is his wont, Spielberg can't resist stuffing the ending of the movie with a bit too much cheese and baloney, at least for my taste. I suspect, though, that, as with "Saving Private Ryan," I will be in the minority in that regard.

Despite those quibbles, "War of the Worlds" is taut, gripping and surprisingly dark filmmaking. It earns its not-to-be-underestimated frights the hard way and not merely by boogeymen who jump out of the closet. Like its blue-collar hero, it works for a living.

WAR OF THE WORLDS (PG-13, 118 minutes) -- Contains violence and obscenity. Area theaters.

Ray Ferrier (Tom Cruise) and daughter Rachel (Dakota Fanning) -- and the rest of humanity -- face an alien invasion in Steven Spielberg's "War of the Worlds."