WITH AN EYE ON . . . : Johnny Galecki, by all reports, is as nice as his David on ‘Roseanne’

Johnny Galecki isn’t letting on if it’s difficult being known as the nicest guy on what many consider to be the most volatile TV set in Hollywood.

Galecki, 20, who plays David on ABC’s long-running “Roseanne,” is “just stupendous to work with ... no attitude,” comments the show’s executive producer, Eric Gilliland, who just can’t say enough good things about the young actor. “He’s just a good guy, not a Hollywood guy, not a smarty rat brat packer. And he’s polite. Huh? A polite person who’s on TV? Yup. He’s very friendly, too.”

All this niceness has certainly made things easier for Galecki, who first met the show’s eponymous star when she cast him in the ABC movie “Backfield in Motion,” which Roseanne starred in with her then-husband, Tom Arnold.

By the time Galecki was brought onto the fourth season of “Roseanne” set--for a guest shot as boyfriend to daughter Darlene (Sarah Gilbert)--he was completely intimidated. “This was a show I watched with my family,” the Chicago native enthuses over lunch at a Los Angeles restaurant. “I was overwhelmed, standing on the stage of a show, working with actors I was a fan of.”

The writers, Galecki says, picked up on that intimidation, which became part of David’s personality. David, the observer, remains the normal one in a TV family prone to histrionics.

In the show’s eighth season, after many episodes touching on their long breakup, David and Darlene are back together. During his interview and even at press time, neither Galecki or Gilliland knew what would happen with the show’s story arc in what may be “Roseanne’s” last season. Both comment, with some hesitation, that not knowing details of scripts from episode to episode is common on the series.

Galecki says that throughout Gilbert’s absences (the actress attends Yale), he often wondered why David was still living in the Connor home. Now he’s glad the couple are back on track. Galecki enjoys working with Gilbert, his best friend on the set.

“David and Darlene are pretty cut and dried,” he explains over a bowl of soup, two packs of cigarettes within arm’s reach. “Darlene is a very strong, loud, opinionated person. David is very passive and and he’s completely head-over-heels in love and worships the ground she walks on.”

Says Gilliland about their on-screen chemistry: “Sarah and Johnny are good friends, so they enjoy working together. When they got back together, made up and shared a big romantic kiss at the end of the episode, [the studio audience] went nuts. They love them together. David’s really good for Darlene. She can be very dark and harsh and there’s a sweet boy in her life, and it’s a good combo.”

Galecki, producers say, fits well into “Roseanne’s” powerful ensemble.

“The writers like him a lot and for writing’s sake, we don’t have to do jokes for him,” says Gilliland. “His comedy is all attitude and character. Roseanne and Sarah do great jokes and with Laurie [Metcalf] and John Goodman and Johnny, it’s all situation and character. It’s a fun way to write and it’s more interesting.”

Galecki has the writing bug himself but, he says, “You just don’t know. Maybe two weeks from now I’ll want to drive across the country or something.”

The actor has done his share of traveling. Born in Belgium, where his father was stationed in the Air Force, he began acting at 7 in Chicago theater productions.

His resume grew with theatrical roles (“Prancer,” “National Lampoon’s Christmas Vacation,” “A Night in the Life of Jimmy Reardon”) and movies-of-the-week. He co-starred opposite Neil Patrick Harris in NBC’s “A Family Torn Apart” in 1993, and was cast in a couple of series (ABC’s “Billy” and NBC’s “American Dreamer”).

In the future, Galecki may look for roles far removed from David but, for now, “It’s really nice to know the work you do every day is going to be seen and, hopefully, appreciated by people you know.

“I can’t imagine myself doing anything else right now,” Galecki offers. “I don’t even know if I can do anything else. So right now, I’d have to say that I’ll just keep on doing what I’m doing, and that’s acting.” And being a nice guy.

“Roseanne” airs Tuesdays at 8 p.m. on ABC.