"Scooby-Doo," at least in my lifetime, has never not been on.

Thirty-plus years ago, I watched the cartoon show as a toddler in our darkened family room on Saturday mornings spent in deep Froot Loop delicto. It played every afternoon in the dorm when I was a pretentious undergrad in the 1980s and I wrote a short paper examining the show as a metaphor for the sexual revolution. Semiotics aside, the professor wasn't amused, even as she must have known her Ghosts, Pop Culture and Religion course couldn't help but attract the slight aroma of reefer madness. (In the Shaggy archetype, what young man cannot detect a template for Zen living?)

Deconstructing "Scooby-Doo" was a drunk, tiresome, though entertaining, component of turning 18 in the Reagan Age. There was a certain nihilism to life, and Hanna-Barbera cartoons were a balm.

And it goes on. As a full-fledged grown-up, I'm as baffled as anyone by Scooby's durability. There are reruns, new cartoons, heaps of merchandise, an amusement park. This dog plays well with all children, and seems particularly loved by the urban hip-hop milieu, which makes me wonder if the original cartoon might have been, to some extent, subliminally black.

All this immortal iconography is certainly not what Messrs. Hanna and Barbera could have envisioned, but these things have a way of evolving all on their own. Given the dreck that it draws from, director Raja Gosnell's big-screen "Scooby-Doo" is indeed awful, but it is awful in a wonderfully crass, burp-and-flatulate kind of way.

Do as I did and see it on a Saturday morning in a theater packed with 7-year-olds: Blundering about for clues in a broken-down fun house ride, Scooby and Shaggy engage in a spontaneous gas-expulsion contest. You don't want to love this, but you will.

Although "Scooby-Doo" falls far short of becoming the "Blazing Saddles" of Generations X, Y and Z, it is hard to resist in its moronic charms. Both as homage and satire, it deepens characters who were never meant to be more than fluff. This gets irritating by the movie's end, but in the first 20 minutes "Scooby-Doo" is pure fun. (Attention, blurb writers: "PURE FUN!!!" -- The Washington Post.)

In the opening sequences, Mystery Inc.'s four quasi-teenagers and one speech-impaired Great Dane part ways because of creative differences in sleuthing. Brainy, bespectacled Velma (Linda Cardellini) embarks on "a voyage of self-discovery"; Fred (Freddie Prinze Jr., performing below even his standards, only blond now) writes an inspirational autobiography ("Fred on Fred"); danger-prone Daphne (Sarah Michelle Gellar) masters tae kwon do and seeks work as a private detective.

Only Scooby-Doo and his master, Norville "Shaggy" Rogers, have remained companionable, doing what they do best. They are parked at the beach in the beflowered Mystery Machine van. Smoke is pouring out of all the windows while "Pass the Dutchie" is on the radio. This is all anyone from my age group really wants to see in a "Scooby-Doo" movie -- the pot jokes. The show has been unintentionally broadcasting certain themes all along: Dog and owner are potheads with eternal munchies. At this rate, how long can it be until we get a Velma lesbian reference, or a hot, sweaty Fred/Daphne sex romp?

Ah, but this is where the makers of "Scooby-Doo" have done the smart and safe thing, both in terms of taste and capitalism: The smoke in the Mystery Machine is coming from a barbecue grill inside. Velma gets a boyfriend. Fred and Daphne are chased, yet chaste. The movie is, as it should be, for children.

The gang is lured back together to solve one last crime. They travel to Spooky Island -- a sort of MTV Spring Break amusement park and tropical hell -- where the owner (Rowan Atkinson) believes a mysterious curse is turning his teenage clientele into zombies. There is much to look at, and although "Scooby-Doo" suffers from terminal idiocy, it's also safe to say that it has more forward momentum than any popcorn movie so far this summer.

As with "The Brady Bunch Movie" before it, the heroes of "Scooby-Doo" are oblivious to their own outmoded ways. Velma's orange knee-high socks, Daphne's go-go boots, Fred's ascot, the fact that none of Spooky Island's teen revelers would say the word "zoinks" -- it doesn't matter to them.

Anachronism is but one pitfall of this genre: The cartoons done live never look as if they belong in the world, because they don't; they look like elaborate Halloween costumes. In the last decade, Hollywood has brought life to everyone from Fred Flintstone to Dick Tracy to Inspector Gadget to Josie and the Pussycats, and yet all of them seem to have died in the process. "Scooby-Doo" gives you the creeping suspicion that, somewhere in Hollywood, someone is taking a meeting about making a slightly ironic Smurfs movie.

Scooby-Doo (listlessly portrayed here by the computer that drew Jar Jar Binks) isn't the star, though he is given lavish camera time and affection on a scale of deification comparable to Michael Jordan's (in that movie he did with Bugs Bunny).

Rather, "Scooby-Doo's" real star is Matthew Lillard, turning in a highly accurate and intensely sublime performance as Shaggy. By the end of "Scooby-Doo," I was convinced I would watch most of a movie just about this character -- perhaps there's time to work him into the sequel, "Seriously, Dude, Where's My Car?" In Shaggy we have Western civilization's greatest scaredy-cat, the original slacker writ as Cassandra. Cardellini's Velma is a treat as well, losing her glasses, exclaiming "Jinkies!" and deciphering hieroglyphics with her Vassar-style pluck. When Gellar and Prinze wander off (as Fred and Daphne are wont to do), we forget about them entirely. A cameo by the much-loathed Scrappy-Doo (who was added to the cartoon in the late 1970s) is livened only by a urination sight gag.

So it's clear from the puppy pee what we're dealing with here. The movie is rounded out only with rap songs and dog piles of special effects.

The real mystery is why children are still drawn to the badness of the original TV show. In "Scooby-Doo's" time, there was something bold about a cartoon in which four teenagers were allowed to drive around in a van at all hours of the night and trespass wherever they wanted.

Then as now, the dog stood for basic values: friendship, loyalty, easygoing humor, common sense in the face of danger. He also preached a message of gluttony and the purest pleasures. It was 1969, and to underline the social unrest of the times, the teenagers would always rip the mask off an authority figure who'd turned to crime. ("And I would have gotten away with it, if it hadn't been for you meddling kids" . . . this line is of course part of the movie, at more than one juncture.)

The essential Scooby worldview remains pleasantly intact: Kids should meddle, dogs are sweet, life is groovy, and if something scares you, you should confront it.

Also, smoke will come out of your ears when you eat a whole jar of chili peppers with a peanut butter sandwich.

Scooby-Doo (87 minutes, at area theaters) is rated PG for light comedic crassness and scary situations.

Matthew Lillard, eerily, spookily, uncannily accurate as Shaggy.