FROM PHILLY TO BEL-AIR AND BACK AGAIN

“The Fresh Prince of Bel-Air” is going home to Philly.

How long he’ll stay is up in the air.

But if you’re a fan of NBC’s popular Monday night sitcom starring Will Smith (a.k.a. Grammy-winning rap music artist Fresh Prince and Will on the show), you know it’s a big deal why he left home in the first place.

The story has been played out in the show’s opening theme for four seasons: Will got into a hassle in a basketball game with some street tough and his mom protectively whisked him off to live with his rich uncle in Bel-Air.

Now he’s going back.

The May 23 episode, “The Philadelphia Story,” is the finale to what promises to be a major month for “Fresh Prince.”

It all begins Monday with a show featuring special guest star Ben Vereen as the father who walked out on Will and his mom. It’s a half-hour that Smith, 25, calls “the most powerful ‘Fresh Prince’ ever.”

Speaking from his home in Los Angeles, Smith--who won raves for his starring role in last year’s film version of “Six Degrees of Separation”--says it was the first real opportunity to test himself since the movie. “I discovered a new level of depth in my acting ability,” says Smith.

The result?

“There wasn’t a dry eye in the house at the end of this show.”

The concept, like many others on “Fresh Prince,” began with Smith, who says Vereen’s warm persona made him the perfect choice.

“You know, you just like him,” says Smith. “I thought that was very important to see in the character who plays Will’s father, and to be able to see where Will got it from. And then, also, because he’s been gone for 15 years. In order for the audience not to hate him for having done what he did to Will, I thought that he really needed to be a character who was someone you could listen to ... before you passed judgment.”

Though Will’s father, a trucker, returns, inviting his son along on a cross-country trip, by the end of the episode he has left his son behind--disappointed yet again.

“It’s an interesting commentary about fatherhood,” says Smith, explaining that for all intents and purposes, Uncle Phil (James Avery) is Will’s father.

“It’s just a really, really warm story,” he says.

The following week involves a bit more traditional sitcom fun as Donald Trump and Marla Maples-Trump stop by after Uncle Phil and Aunt Vivian (Daphne Maxwell Reid) put their house up for sale.

Smith reports back that “Marla was great” but that “Don could use a little work.” Smith had originally hoped to have “Beverly Hills, 90210” producer Aaron Spelling and his family stop by, too, because there has been a running joke on “Fresh Prince” about the Spellings’ living next door. But the Spellings weren’t available.)

Undoubtedly, though, it’s the return trip to Philadelphia that’s most likely to be the freshest “Fresh Prince” ever.

As usual, Will’s cousins Carlton (Alfonso Ribeiro), Hilary (Karyn Parsons) and Ashley (Tatyana M. Ali) resist. “Yuck, Philadelphia,” says Ashley, when the idea of a family trip is brought up. “We might as well be staying in the United States.”

And, as you might expect, Will’s homecoming isn’t immediately ideal.

For starters, he finds out--because he skipped town rather than fight--that the locals have named a chicken sandwich after him. So Will decides to fight.

“I gotta get my rep back,” Smith explains. “And the only way I can get my rep back is to beat up the guy who beat me up.”

The season will end and begin with the show still set in Philly, which Smith gives a winking, 50-50 chance of staying put. (But don’t count on it.)