The planet, we are informed, is warming. The ice caps are melting.

Climates are changing. Scientists blame factory smokestacks, car exhausts andthe destruction of the rain forests. ``The Arrival'' has a more terrifyinghypothesis to explain the phenomenon. In the great paranoid tradition of science fiction, the discovery ofthis possibility is made by one man who cannot get anyone to listen to him andwho grows desperate as the establishment slams its doors. The man is ZaneZaminski (Charlie Sheen), a radio astronomer who listens for signs ofintelligence from outer space. Unlike his colleagues, he's looking in the noisyFM band: ``It's like searching for a needle,'' his partner tells him, ``in ahaystack of needles.'' When he picks up an unmistakable signal, Zane takes itgleefully to his boss (Ron Silver), only to be told that the government's entireintergalactic eavesdropping operation is being scaled down because of budgetcutbacks. Zane's frustration is the engine for a science-fiction film ofunusual intelligence that keeps on thinking all the way to the end, springingsurprises and ideas. The movie is as smart as ``Mission: Impossible'' is dumb.

``The Arrival'' is always clear about its science, its plot, its characters andits meaning, unlike ``Mission: Impossible,'' which is concerned with surfaceflash, visual impact and action. (That's not to say ``Mission: Impossible''isn't entertaining; I am simply making the comparison.) Zane is dumped from his job but cannot shake the conviction that hedid indeed hear an intelligent signal from another planet. He's kind of a nerdwith a goatee and a pocket protector, who can duplicate a science lab in his ownattic with a couple of good computers and a soldering iron. Aided by a smart kidfrom next door (Tony T. Johnson), he soon has his own listening station up andrunning. His method for duplicating a big government radio telescope isingenious: He gets a job as a repairman for consumer satellite dishes, secretlywires them into a network and puts together his own ``phased array'' to listento space. I have no idea if this would work, but I like his attitude. His investigation of the signals leads him to Mexico, where heencounters another scientist, played by Lindsay Crouse. We've seen her in thefilm's splendid opening sequence, which begins with her sniffing a flower in ameadow, and then pulls back to show the meadow surrounded by thousands of squaremiles of arctic ice. Together, they speculate about global warming and itspossible connection to the strange situations they encounter in a small centralMexico village. At one point, frightened by where her reasoning is leading her,she sighs, ``I get so damned apocalyptic when I drink.'' Read no further if you plan to see the film. What I appreciated about ``The Arrival'' is that it stays with itsthesis all the way to the end. It has a chilling hypothesis: Earth is being``terraformed'' by an alien species that would prefer the planet a little warmerbefore it moves in. Combining this idea with a touch of ``Invasion of the BodySnatchers'' and some ambitious special effects, ``The Arrival'' springssurprises on us right to the end; the screenplay is by David Twohy (``TheFugitive''), who also directed, and who doesn't run out of steam. Consider, for example, a clever little spinning globe that seems towork as a vacuum cleaner, sucking everything into another dimension. The job itdoes on a gigantic radio telescope is one of the best recent examples of specialeffects. There is a shot when Zane's fiancee (Teri Polo) rolls to the edge ofthe big dish; at first, all we see is its vast white expanse, and then suddenlywe see the earth below, spread out beneath her. The way the shot is constructedmakes it into 10 seconds of just about perfect cinema. A lot of movies in this genre break down in the end into asimpleminded series of chases and fights. There are fights and chases in ``TheArrival,'' but they're generated by the plot and punctuated by revelations andpossibilities, so that the movie keeps on thinking and doesn't go on automaticpilot. ``The Arrival'' fulfills one of the classic functions of sciencefiction, which is to take a current trend and extend it to a possible (andpreferably alarming) future. Unlike ``Species,'' which assumed that alieninvaders would be monsters (or, if you read the film differently, would sendmonsters ahead to clear the way for them), ``The Arrival'' gives its alienscredit for reasoning that we might almost be tempted to agree with. ``We're justfinishing what you started,'' one of the aliens tells Zane, referring to thesmokestacks, auto exhausts, rain forests and so on. ``What would have taken you100 years will only take us 10.'' He, or it, has a point.