'Gamble-Huff-Bell Music."

The first two names listed on the sign above the doorway at the Philadelphia International Records offices at 309 S. Broad St. are those most closely associated with the sophisticated soul music that became universally known as "The Sound of Philadelphia" in the late 1960s and early 1970s.

But there were more than two major players writing the Philadelphia chapter in the great American soul-music history books.

Along with Philadelphia International Records owners Kenny Gamble and Leon Huff, there was also Thom Bell, the producer, arranger, and songwriter known for the delectably sweet music he made with the Delfonics and the Stylistics.

Of the Mighty Three - the name of their joint publishing company - Bell's name is not quite so synonymous with the Philly sound as Gamble's and Huff's. That's in part because, rather than come in as a partner when the duo formed PIR in 1971, he carried on as an independent producer for the Spinners, Dionne Warwick, and Elton John.

And it's partly because the Kingston, Jamaica, native has lived on the West Coast since the 1970s. He currently resides in Bellingham, Wash., where, he says, he's more likely to see a mountain lion or peregrine falcon than a cheesesteak. He doesn't fly and rarely travels home to the city where he was raised.

But, "Betcha by Golly, Wow," there on a recent afternoon at the PIR offices was the elusive Thom Bell. Not only in a publicity shot on the wall from 1962 - when he was a member, along with Gamble, of Kenny & the Romeos - but also in the flesh, seated at a conference table, talking about past triumphs and future projects.

"He came to my house on Parrish Street in West Philadelphia so my sister could help him with his homework," says Bell, 70, remembering how he first met Gamble. (Gamble and Huff were later to bump into each other in an elevator in the Shubert Theatre, now the Merriam.) "I was there practicing at my piano. He said, 'You play piano? I write songs.' I said, 'Really? Maybe one day we'll get together.' "

When they did, they found they were naturally simpatico.

"That's the way it was with these two, too," says Bell. "And that's the way it happened with Linda Creed and I," he adds about his late partner, with whom he wrote "You Make Me Feel Brand New" for the Stylistics and "Rubberband Man" for the Spinners.

"It's like you and your wife, your mate. You know when it fits. There are not too many people you can ride the ethers of life and love together with. You're lucky if you can do it by yourself, twice as lucky if you can do it with a partner." He looks across the table. "When the three of us got together, it was like hand in glove."

"Like magic," says Gamble.

Three years ago, the PIR building, which housed the offices of Cameo-Parkway records before Gamble, Huff, and Bell bought it in 1970, was damaged in a fire, though the studio - where G & H's first songwriting collaboration, Candy & the Kisses' "The 81," was recorded in 1964 - was unharmed. This trip back east via train was Bell's first look at the damaged building ("It's bad," he said) and for the partners, who are now signed with the William Morris Agency with an eye to preserving their legacy, to discuss future projects. "We're doing a book together," says Gamble. "And there's talk of a [Sound of Philadelphia] stage play. ... "

"Like Jersey Boys," says Huff.

"There's a lot of interest," adds Gamble. "Plus, we're trying to wrap up some business with the fire."

The Mighty Three meet-up was also a chance to consider why the smooth, sleek Philly sound has proved so durable, from Harold Melvin & the Blue Notes' "If You Don't Know Me by Now" to the Three Degrees' "When Will I See You Again" to the O'Jays' "Love Train," still played incessantly in Coors Light ads on TV.

"We all came from humble beginnings," says Gamble, 69. "The music was our passport to travel the world in our minds. We all had a desire to accomplish something in the music industry. And then we realized we could work together, rather than work apart."

When the trio were hustling in the early '60s, they were frustrated by their inability to get work at Cameo-Parkway, the white-owned dominant label in town.

"There weren't too many chocolate folks working in this building," says Bell. Adds Huff, 71: "There were African American artists. The Orlons, the Tymes, Chubby. ... "

"But there were no African American producers or administrators or musicians," recalls Gamble. "That was the difference. When we came in, we opened the doors to everybody. We had no fear of people."

Indeed, their "Message in the Music" heyday was marked by racial cooperation in a time of social upheaval. Black songwriters worked with black and white musicians, string players from the Philadelphia Orchestra crossed Broad Street to record with African American arrangers like Bell and Bobby Martin.

"It was like a school," says Gamble. "A lot of people got their start here. We were dealing with the human race. We weren't dealing with that madness that comes from separation. You get more out of everything when you blend stuff together."

For all that the Mighty Three have in common, there are clear distinctions. Bell's music is lighter than cotton candy (though rarely too sticky sweet); Gamble and Huff's tunes are more rugged, earthier.

"The stuff I do goes to the heart," says Bell, who is of the opinion that "the only two things you can write about are love or escape."

What Gamble and Huff "write goes to the soul. The Stylistics go to the heart." He sings a few bars of "La La (Means I Love You)," then lowers his voice: Teddy "Pendergrass goes to the soul."

The key to the music's longevity, says Gamble, is the collaborative spirit with which it was made.

"The reason it still sounds good is we worked as a team. I'm very thankful," he says. "But the reality of it is, we always used to say, 'Let's make classics.' That's what we were shooting for. I'm just glad we hit that mark."