For Steven Williams, taking over the role of Capt. Adam Fuller from Frederick Forrrest, who had it for the pilot, "has been like a Christmas miracle."

Williams plays the mentor of four young undercover cops, the man who holds their sometimes off-the-wall activities together.

To prepare for his role, Williams rode the 3-to-midnight shift with a police sergeant from the Southeast Precinct in Los Angeles. "We went through the roughest neighborhoods: the projects ... violence, drugs, you name it."

Williams spent part of his own childhood in the housing projects of Chicago, where he lived with his mother. But sometimes he lived in Flint, Mich., with his father, an automotive plant foreman, and in Memphis, Tenn., where he spent his early years with his grandparents.

"That kind of growing up gave me different insights. I'd be away in the summer. It was a ghetto kind of life, but my mom didn't have a bunch of kids to provide for. A lot of times I felt like I was privileged because was I the only one."

In Chicago, before he got into show business, Williams worked as a mail carrier -- "my second-best job ... it was wonderful, in the summer. After my first winter in Chicago, I thought 'I've got to get out of this business.'" He worked in a jeans boutique and then at two Michigan Avenue shoe stores, "wearing a suit and tie and being charming to upper-class ladies."

Eventually he began to do "catalogue shoots, advertising. I did voice-overs, industrial films. Then I started to do stage work. I worked in the Children's Theater Group. I learned to act -- that's the best way to learn to act -- on stage. On-the-job training."

Williams went to Los Angeles in 1979 to do "The Blues Brothers" with Chicagoan John Belushi and Dan Aykroyd, then shuttled back and forth between L.A. and Chicago doing "The Marva Collins Story," "Continental Divide," "Chicago Story" and "Dukes of Hazzard." He appeared in seven other theatrical movies, six television series and several TV movies.

But Williams admits that his career has had its dry spells. "I've had droughts. In '82 I think I worked once in an entire year. I lived on residuals, but there was no work coming in. Just before '21 Jump Street,' I had to borrow money to keep up our mortgage."

Williams was on the initial season of "The Equalizer," appearing on the first seven shows as police officer Jefferson Burnett. "When I left the show, I was very disappointed, but it worked out for me on a show that's just as popular. Right now I could not be happier ... With '21 Jump Street,' I'm more recognized that I ever was. I've had to straighten up a lot of my act. My wife {Ann Geddes, a theatrical agent} and I stopped smoking recently. I don't drink or smoke on camera. I can't go out and get quite as drunk in bars. The kids are out there watching it. You have some responsibility. We're trying to make a social statement. That's what the whole show is about, along with the public service announcement at the end.