ON THE REBOUND WITH BILLY BOB; `A SIMPLE PLAN' THRILLER IS JUST ONE OF MANY THORNTON PROJECTS TO COME.

Byline: Bob Strauss Daily News Film Writer

Billy Bob Thornton is looking good.

Quite a relief. He had us worried there for a while.

Bright-eyed, solidly built, with his hair dyed a vibrant, platinum blond, Hollywood's redneck renaissance man even has the country glam look down to a T: simple but elegant leather jacket, indigo blue jeans, hand-tooled pointy boots and the signature gimme cap, this one courtesy of the Arkansas State Police.

We know Thornton doesn't really look like the backwoods grotesques he specializes in playing: ``Sling Blade's'' brain-damaged killer Carl, ``U-Turn's'' twisted Twister-playing grease monkey and now Jacob Mitchell, the dim-bulb Midwestern geek in the acclaimed new thriller ``A Simple Plan.''

We saw him looking good in a cowboy tux at the '96 Oscars, where he won a screenwriting award for ``Sling Blade,'' which was also Thornton's directing debut. He was even pretty natty as the harried NASA director in this year's biggest commercial hit, ``Armageddon,'' and his competition in that one were the hunky likes of Ben Affleck and Bruce Willis.

But real-life Thornton sightings earlier this year presented a more alarming vision. He had become exceptionally thin, prompting speculation about dire illness.

Nothing of the kind, Thornton happily reports. Well, maybe a little, mentally.

``I lost a lot of weight,'' he says in a friendly Ozark drawl. ``I'm at my regular size that I've been all my life now, around 160 pounds. For `U-Turn,' I was 197, and when I did `Pushing Tin,' which is this black comedy about air traffic controllers, after `Simple Plan,' I was 138.

``That was by design, I wanted to do it. But I had a few articles come out - `What's the deal with him? Is he sick?' No, I just got too skinny. But frankly, for a while there, I think I had a little mental problem. I got anorexic; of course, I denied it to my girlfriend and everyone else who said I had an eating disorder.''

A common enough affliction, but strange to hear coming from Thornton. Especially in the context of discussing ``Simple Plan's'' Jacob, a bucktoothed, nearsighted bumpkin with an army surplus wardrobe and hair oily enough to lube his broken-down pickup.

``Well, in the movies, I have no vanity,'' he says with a laugh. ``I, frankly, love playing characters that are different, that look odd or are odd. That's the fun of it for me. I mean, `Armageddon,' when I had to play a character like myself, I was freaking out. It was the hardest thing I've ever had to do.''

Hard maybe, but good enough to impress producer Jerry Bruckheimer, who makes a point of casting his high-octane action spectaculars with the finest actors he can get. ``Billy Bob's the real deal,'' Bruckheimer says. ``He's a wonderful actor, and he adds credibility. He was the glue in `Armageddon,' held the whole thing together, because every time you cut to him you knew he was the real deal. And a lot of that was based on the way he looks.''

Looks again. But it's Thornton's ability to bring out the unseen qualities of a person's soul that distinguishes his on-screen work.

Listen to him discuss Jacob's real motivations when, with his educated brother Hank (Bill Paxton, who starred in the acclaimed, Thornton-scripted ``One False Move'') and his unemployed only friend Lou (Brent Briscoe), he discovers a cache of $4.4 million in a snow-covered plane wreck.

``Jacob's got one friend; he wishes his brother would be as close to him, but the brother's a little ashamed of him,'' Thornton observes. ``He longs for family, and I think he's just trying to gather it all in. Everything's too scattered; he wants a home. And, he figures, if he can have money, people will like him.

``It's actually what I thought as a kid in Arkansas, where we were pretty poor,'' he adds. ``I thought, if we had money, I'd be included more, the popular kids would ask me to their parties or whatever. I think we're told from an early age, `Yeah, if you have money, you'll do OK.' ''

It took a long time for Thornton to learn firsthand that money doesn't change everything. ``I came out here in my early 20s,'' says the 42-year-old actor, who initially pursued a career in music. ``And I was definitely like a novelty to people, being from the South and everything.''

After years of eking out a living in bit parts, he finally got a regular role on the sitcom ``Hearts Afire.'' Around the same time, his script (co-written with Tom Epperson) for ``One False Move'' garnered widespread praise.

Then ``Sling Blade'' laid the formerly amused Hollywood at Thornton's feet. In the two years since, he's acted in six released features (``Primary Colors,'' ``The Apostle'' and ``Homegrown'' among them), has ``Pushing Tin'' in the can and just finished directing his second, self-starring feature, ``Daddy and Them,'' a film about, among other things, male vanity.

In February he'll begin his first directing-for-hire film, and it's a doozy: an adaptation of Cormac McCarthy's best-selling ``All the Pretty Horses,'' which will star Matt Damon.

But with massive professional success came at least one big personal crisis. Shortly after Thornton won his Academy Award, his fourth wife, Pietra, filed for divorce. Charges of violence and intimidation were very publicly flung. These days however - at least in public - Thornton sounds nothing but compassionate toward his ex-wife, with whom he has two young sons.

``When somebody all of a sudden gets famous and there's something going on, I know it's a great thing to talk about,'' he says, his voice growing weary. ``But all we care about in my family is raising these kids right. That's what we've done. All that other stuff is gone, and the influence of that is nonexistent to me.

``The situation is great. God bless anybody from my past, I wish them happiness and peace forever.''

Now in a rewarding relationship with actress Laura Dern, Thornton admits that, despite the occasional blip on his own happiness radar, things are looking pretty good.

``The overall shape of things is great. Yeah, I love things.''

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Photo: (1--2) Billy Bob Thornton, recovering from the breakup of his fourth marriage and wildly fluctuating weight, both following his Oscar win for ``Sling Blade'' (he was down to 138 after ``A Simple Plan,'' top left), says things are now looking better.