WHATEVER "it" is, Brad Pitt has it in spades. The guy fairly drips charisma and goofy sex appeal; his wayward brother in Robert Redford's current "A River Runs Through It" combines the classic good looks of a young Redford and the playful, conspiratorial attitude of the young Paul Newman.

Come to think of it, Pitt is Butch and Sundance rolled into one.

Little wonder producers and writers are racing to customize whatever they've got hanging into "the new Brad Pitt vehicle." So far this year, besides "River," the 28-year-old heartthrob has been seen in Ralph Bakshi's coolly received "Cool World" (as the toon-town shamus) and in the seriously weird fable "Johnny Suede" (as a Ricky Nelson wannabe with a rooster-like pompadour).

Upcoming is the thriller "Kalifornia," wherein Pitt teams with current steady Juliette Lewis. He plays a man on the run named Early Grayce. "He's this serial killer guy . . . pure white trash," Pitts volunteers, flashing that mischievous smile.

Though he had done some episodic TV work, filmgoers got their first good look at Pitt last year. And it was a lulu, a career-making walk-on in a little something called "Thelma & Louise." Pitt played J.D., a hitchhiker who inveigles a ride with his lanky good looks and cocker-spaniel eyes. Like Pitt characters to come, J.D. is the kind of con artist everybody likes to be conned by.

The quirky road picture took off unexpectedly, and so did Pitt's career.

''It was that kind of part," says the actor, still sporting his "Kalifornia" beach look (beard and long hair). "I had been waiting, looking for the part. I knew that's what it would take. And when several guys (director) Ridley Scott wanted fell through, they took a chance with me."

Awaiting him was more of the same -- a career's worth of wayward travelers, wayward brothers and wayward buddies.

''I knew I had to show them what I could do next," he says after the Toronto premiere of "A River Runs Through It." "You have to find a balance, or you'll be playing hitchhikers for the rest of your career."

And so Pitt threw in with Redford, who was closing in on his dream of making Norman Maclean's autobiographical "A River." Pitt auditioned -- "badly," by his own admission. Redford, who hadn't seen Pitt in "Thelma & Louise," liked the young actor's non-threatening swagger, but he wasn't sure. Maybe Pitt looked too much like the young Redford.

''I just heard Redford was doing a film about two brothers in Montana," says Pitt, pulling on his second Malboro Light of the interview. "That's all I knew. But that was enough. I had to be in it -- even if the audition didn't go very well."

Pitt needed insurance. So he got together with actor buddy Dermot Mulroney, found a mountain river north of L.A., and taped himself knee-deep in water, playing Norman Maclean's ill- fated younger brother. He called on another buddy, Melissa Etheridge, to compose some music.

Such resourcefulness -- a Pitt trademark -- paid off. Redford cast Pitt opposite Craig Sheffer (who plays Norman as a young man), Emily Lloyd (Norman's girlfriend) and Tom Skerritt (the boys' Presbyterian minister father). As for the fly- fishing, an integral part of the story, that came more easily than he expected.

''There's a rhythm to casting," he says. "They taught me the mechanical things. How to hold the rod, grip the reel, etc. And all of a sudden I found myself in this (casting) rhythm. It just kicked in."

Regarding Redford: "He's good people. I got the feeling when we spoke that this ('A River') went way past just making a movie. It was something very personal that kept the man going. It was some great passion." Pitt has been in awe of the actor- director for as far back as he can remember.

''I grew up in the Ozarks, outside of Springfield (Missouri). We did typical boy things. We'd hang out in the woods, create our own fun. And we'd go to the drive-in a lot."

And it was at the drive-in -- sitting on the hood of the family sedan, munching soggy home-popped popcorn ("we couldn't afford the concession stuff") -- that Pitt discovered such Redford films as "Brubaker," "Three Days of the Condor" and, of course, "Butch Cassidy and the Sundance Kid."

Pitt has trouble articulating what it is about "A River" -- the book and movie -- that touched him so deeply. But he took a stab at it.

''It just hit me," he says, watching his finger trace a crease in the tablecloth. "You read that last page in the book. . . . It's very personal. This film is like memories for me. Good memories. Of rain. Of sad, cozy times as a kid."

When it's observed that Pitt, at this stage, can do no wrong -- that the arc of his rising star knows no limits -- he becomes a tad uncomfortable. The panache and flash obviously are an act for the camera.

''I'm hot now? No -- c'mon. I just wanted this picture, that's all. I'm just watching and observing. I'm coming up the ladder to where I want to be. I'm not a big analyzer of where I'm going or what I've done. I see it as a waste of time. That way I have more fun."

Besides, he adds, it's more about following one's instincts. "It's just me and my monkeys," is how Pitt put it. "I don't know what brings me to parts."