Ever since 1996's "Independence Day," Smith has been known for action-packed blockbusters ("Men in Black") that open in the heat of summer and make millions.

In fact, he likes to call the July 4 holiday "Big Willie Weekend."

But now that he's 36, he's moving away from action. "My body definitely doesn't feel the same," he admits.

He says he'd like to avoid "that old-man run - where you see the action hero in his 50s, and he wants to make one more, but shouldn't."

That's why he's going back to his comedy roots ("The Fresh Prince of Bel-Air"), with "Hitch," which opens Friday.

It's his first romantic comedy - and if audiences embrace him as a lover boy, it likely won't be his last.

In it, the $20-million-a-movie star plays Alex Hitchens, an ultra-suave New Yorker who's so smooth with the ladies that he hires himself out to other guys as a "date doctor."

Yet while he's trying to help a slobby accountant (Kevin James of "The King of Queens") hook up with a fancy socialite (Amber Valletta), he finds himself falling for a hard-edged gossip columnist (Eva Mendes).

As it turns out, the "Hitch" shoot in New York last summer brought up its share of relationship challenges in Smith's own marriage - though he and wife Jada Pinkett Smith handled them with customary aplomb.

"I mean, wow, Eva Mendes is freaking gorgeous," Smith says - and he insists he would say the same thing to Jada's face.

"Our perspective is, You don't avoid what's natural. You're going to be attracted to people.

"In our marriage vows, we didn't say 'forsaking all others,'" he adds - though he insists he'd never cheat on Jada without asking her permission.

"The vow that we made was that you will never hear that I did something after the fact.

"If it came down to it, then one [spouse] can say to the other, 'Look, I need to have sex with somebody. I'm not going to if you don't approve of it - but please approve of it.'"

Now, that doesn't mean that Will Smith is about to screw up Hollywood's last good marriage.

For him, it comes down to one thing, he says: "Are you a person of your word or not?"

That's the secret, he says, to why his marriage has lasted, while so many other celebrity love matches have bitten the dust.

"I spend hours reading, studying," Smith says. "And my wife and I talk about things that work - and don't work."

Eight years in, the Smiths still behave like newlyweds.

"I don't let a day go past that Jada doesn't feel like the queen of the world," Smith told a reporter last month. "I make sure every single day that she knows how I feel about her."

Will and Jada's solid relationship is such a Hollywood rarity other famous couples have turned to them to help salvage their unravelling marriages.

"Every time somebody in Hollywood breaks up, Jada and I go and find out why," Smith says.

"With Bruce and Demi, we spent hours talking to them.

"And Tom and Nicole - hours, just trying to understand what happened."

Of course, even the Smiths' expert marriage counseling couldn't save either of those relationships - but the experience, he says, has helped them in their own.

Like his good pal Tom Cruise, Smith is someone who prides himself on self-control and serious discipline - not only in relationships, but also in every other part of life.

"It's kind of a game that I play with myself," Smith says. "When everybody else is tired and going home at the end of the day, I need to know that I'm the one person that's going to the gym.

"I need that mindset because I've been successful, and it's easy to get lazy. Once you start to slip physically, you're going to slip mentally."

Smith has been a gym rat since 1995, when he first started working with a personal trainer to get buffed up for "Bad Boys."

These days, the 6-foot-2 actor lifts weights and runs about three miles four or five times a week.

He showed off his buff bod (all of it) last summer, during a brief nude scene in "I, Robot," and America's breathless reaction spurred Jada to redouble her efforts at the gym.

"She said, 'Nope, you're not catching me out there, slipping out of shape,'" Smith has recalled.

"We call the younger guys that might be coming after Jada 'thundercats,' and we call the girls who might be coming after me 'thunderkittens.'

"Jada was like, 'Nope, all them thunderkittens got to see my man in that movie. I gotta go get in shape.'"

Smith has always wanted to please the women in his life.

"I wanted them to always look at me like I was the best," he recalls of his mother and grandmother. "That transferred into the interaction with the women in my life."

When he was coming up, first as a rap star, then on TV's "Fresh Prince" and in movies, Smith met plenty of women - and sowed plenty of oats.

"I had about two years when I went a little wild," he recalls. "After my first girlfriend left me, I just didn't want to be attached. I wanted to be able to have sex and move on."

But that was then.

After splitting from his first wife, Sheree (they have a son, Trey, now 13), Smith met Jada, when she tried out to play his girlfriend on "Fresh Prince." Nia Long got the part, but Jada got the man.

They married on New Year's Eve in 1997, and now have two kids of their own: son Jaden, 7, and daughter Willow, 5.

They also stay very close with Sheree and Trey, in a self-described "blended family" that Jada and Will used as inspiration when they created the UPN sitcom "All of Us,"now in its second seasion.

Will's next big-screen project is an as-yet-untitled biopic adapted from a real story about a homeless man who was living in a train-station bathroom, but now is a self-made millionaire and owner of a Chicago stock brokerage.

And he's also keeping a finger in the music biz. He'll release a new single at the end of February, and an album next month.

He'd even like to go on tour later this year, maybe starting in Europe, where Jada played last year with her band Wicked Wisdom, as an opening act for Britney Spears.

"Jada wants to go back," Will says. "It'll be the Smith family tour."

Just don't expect to find him chasing bad guys or fighting aliens anytime soon.

Even Jaden thinks his father should lay off the action movies.

"He said, 'Whoa, Dad, I love that,'" Will recalls. "'But don't save the world no more.'"