AS A CHILD ACTOR ON TV'S LOST IN Space, Bill Mumy didn't have much time for fun stuff... like comic books or rock and roll. "I had a concept of work, because acting is hard work," says Mumy, who spent three years as young Will Robinson in the sci-fi TV series. Now, at 37, Mumy is catching up.

The only child of a California cattle-ranching family, Mumy entered high school when the series ended in 1968, then spent two years studying music at Santa Monica College. Later acting jobs proved disappointing: a short-lived TV series (Sunshine), a small part in the film Papillon and a siring of B movies.

Mumy calls his Lost in Space years great and credits his parents' investment of his childhood salary for making him financially secure to this day. He lives in a hillside L.A. house with wife Eileen, a childbirth instructor, and son Seth, 19 months. Despite occasional acting jobs (three episodes of Superboy this fall and a film this summer), for Mumy the soundstage has largely given way to the rock stage and the three bands he fronts (Barnes & Barnes, the Seduction of the Innocent and the Generators). In 1985, Mumy teamed up with pal Miguel (Twin Peaks) Ferrer to create Marvel Comics' Comet Man series, and now he's writing a comic based on Lost in Space characters.

Mumy still keeps in touch with most of his fellow Space-mates, and although his TV dad, Guy Williams, died in 1989, he often talks with June Lockhart, his Lost in Space mom. "Every few months I have lunch with Jonathan Hams, who was Dr. Smith," he reports. "Two weeks ago I went to see Marta Kristen in a play. Angela [Cartwright] has a boutique in the Valley." And the robot? "The robot ended up at my friend's house last year," Mumy discloses, "decorated as a Christmas tree."