For 11 years , and a million reruns, Gary Coleman has been Arnold Jackson, the chubby, streetwise waif-with-a-will who wisecracked his way thorough the tailor-made series "Diff'rent Strokes."

For fans, Little Arnold will never grow up.Little Gary has.

At 21, three years after "Diff'rent Strokes" left the network for syndication, coleman has ventured into a medium that fascinates him--radio--and a message that soothes him--the music of the New Age, songs and albums with titles that sound as if they belong on a bookstore's metaphysics shelf.

Last fall, Coleman moved to Colorado, near Denver, and bought a 4,300-square-foot, $470,000 house, since enlarged to accommodate his model train collection. Along with a new Sunday night show on KHIH-FM -- "New Age, light jazz, soft rock" -- Coleman works regularly at a hobby shop in Denver, and lends his name and presence to fund-raising efforts by the National Kidney Foundation of Colorado.

Words like "self-control" abd "perfectionism" speckle Coleman's conversation as he cuts production cartridges and edits portions of his weekly program "colorado High."

Colorado doesn't just record over false-starts, he erases them. "I'm such a perfectionist I don't like having any mistakes lying around. I'm only a perfectionist as far as my job and my craft are concerned -- not in other areas."

Station manager Ross Allie says the timing was perfect when Coleman expressed interest: "We were looking for a show for new music and Colorado artists. We talked about three hours. He's not fluff. He knows the music."

Of New Age music, Coleman says, "touches the soul in a way that moves you. It swings your moods. It makes you feel good . . . it's music that does not attack you."

In February, the day before he turned 21, Coleman filed suit in Santa Monica Superior Court claiming former business manager Anita DeThomas and his parents and personal managers, W.G. Coleman and Edmonia Sue Coleman, diverted an unspecified amount of young Coleman's assets to themselves.

"I can't really discuss that because the attorneys are handling that," Coleman said.

Of his parents, Coleman says, "They raised me for 18 years. And that's what their job as parents is supposed to be, and they did their job, and I love them for it, and they still love me, and I still love them. If there's anything I ever need or anything I need to talk about that only a parent can talk about with their kids, then I can always call them."

The show business career that bloomed with "Diff'rent Strokes" when Coleman was 9 actually began much earlier, with fashion shows in Chicago.

"A mall manager thought I had talent, and he gave my parents a card to an agency. I made up my mind to try it and see if I liked it or not, so I did a couple of commercials."

Talent scouts saw those commercials and "they thought there was a commodity there. So I made up my mind to do "Diff'rent Strokes" and see what happens. We all see what happened. I don't think it will ever be another "Lucy," but it's going to be around for at least another eight years before people get bored with it."

As for the radio show, "I'm doing it because I enjoy it. I don't want people to get the wrong impression and say `Oh, he must be broke.' That's not the case. I work at the radio station so that I can support the National Kidney Foundation with some of that money. Part of my check goes toward that."

He contributes to the kidney foundation because of the problems he has had. After two kidney transplants and years of medicine to suppress rejection, he also knows there is a third transplant in his future.