Jay Underwood turned 19 this month and concedes that, yes, so far things are looking good even though this week he shows up in an ABC Afterschool Special wearing lipstick and eyeshadow, leather and chains.

For a guy whose agent is promoting him as "the new teen-age heart-throb," he's got a bit of a strange role, playing an ordinary-looking high school violinist who decides to change his appearance -- but not his personality -- in "The Day My Kid Went Punk" (Wednesday on WJZ, Friday on WJLA).

Rising star Underwood has turned up within the past month in two episodes of "A Year in the Life" and the opener of "J.J. Starbuck," with Dale Robertson and Patty Duke, both new this season.

Last June he was a teen-age robot in "Not Quite Human," with Joseph Bologna, for The Disney Channel; has appeared in a feature film, "Desert Bloom" with Jon Voight and JoBeth Williams, and played a reclusive orphan in a TV movie, "The Boy Who Could Fly." He's appeared in producer Robert Redford's "Promised Land" and is working on a new film, "The Invisible Kid," with Karen Black (she plays his mother) due out in early 1988. Last summer he turned up in black tux as an ACE (Award for Cable Excellence) presenter.

Success brings its own rewards, of course, and after sharing an apartment in Malibu with an actor-friend for the past year, he's now looking for "a great one-bedroom apartment with a city view in Laurel Canyon or Hollywood Hills," he said last week.

Underwood's path to Los Angeles took him from his home in Hayward, in San Francisco's East Bay area, to Minneapolis, where he attended a performing arts high school that was affiliated with the Minneapolis Children's Theater Company.

The son of a California highway patrolman, Underwood said he got his start in acting when he went along with his younger sister, Julie, to community theater auditions. She eventually gave up the idea ("she's going to save the whales"), but he got the role of the Big Bad Wolf in "Little Red Riding Hood" and was so taken with acting that he went over to the American Conservatory Theater in San Francisco for lessons. There he was cast in "A Christmas Carol."

Meanwhile, his father thought that a television series airing then, "CHiPS," was maligning his profession. "He hated that show with a passion because it was so unrealistic," said Underwood. "But all the biker guys in his office loved it."

At 13, Jay went off to Minneapolis for a five-week summer session, then returned the following summer with his parents' blessing and stayed on for high school. "At 14, I basically left home," he said. He missed the camaraderie of his family, he said, and fishing trips with his dad, but "I ate, slept and breathed theater." He appeared in the school's productions of "Secret Garden," "Madeline and the Gypsies," "The One That Goes Out" and "The Tattered Trunk."

Mornings he attended academic courses plus classes in dance, acting and singing; afternoons he auditioned for and acted in productions along with the other students. "I got a great education," he said. "My SAT scores came out fine, and I got accepted at New York University." But show biz was calling, so he gave up college in favor of beginning his career.

His sister, now 16, is still in high school back in Hayward. "I think at first it was kind of hard for her to deal with ... but I think she's proud of me." His parents, Roger and Carolee Underwood, are proud of him too, although his father reportedly was unsettled when his son came home wearing a diamond earring.

In "The Day My Kid Went Punk," Underwood plays a rather shy teen-age violinist named Terry, who's growing up between an outgoing older brother and a precocious younger sister. "He's the middle child in the family," said Underwood. "He feels left out, he feels neglected. He decides it's time for him to get a little attention -- and he does that by going punk. But he's still the same, nice Terry, who plays the violin in the school orchestra." The show's message, he said, is essentially that "you can't judge a book by the cover."

Bernie Kopell, formerly of "The Love Boat," and Christina Belford play Terry's parents. She's an associate professor of psychology who's moderating an educational conference on "The Boy George Syndrome and How to Avoid It." When her son turns up as a punker, she overcomes her surprise and invites him and his hard-rock musician friends to be guest panelists.

Fern Field, writer, producer and director of the special, said she became interested in why teen-agers "go punk" after she heard Cyndi Lauper talk at a Women in Film awards presentation about her family's reaction to her appearance.

In interviews, Field found that one of the reasons boys adopted the style was because girls like it. But almost inevitably, she also learned, their parents had trouble accepting the change, even though it might be merely one of appearance.

"Everyone I talked to had some story to tell about their kid or relative going punk," said Field. "I didn't realize how prevalent it was until I got involved in writing this story."

Scholastic Magazine, which circulates among schoolchildren, apparently does. The magazine is featuring the show in its Oct. 16 edition.

But most of the audience watching ABC's Afterschool Special this week are too young to remember the original punks. And it's fairly certain none of the original punk-rockers will either watch the ABC special or read Scholastic magazine.

The British punk-rockers of the late '70s were a tough bunch. They rallied round a rock group called called the Sex Pistols, its lead singer, Johnny Rotten and its bassist, Sid Vicious. Mainly lower-class youth, often unemployed school drop-outs, they pierced their cheeks, ears and noses with oversized pins, wore leather and chains and sometimes used glue to form their artificially colored hair into spikes.

For them, appearance was one with lifestyle, hostile and alienated from mainstream British society. Then, of course, there was no make-up, and no violin-playing in any school orchestra, either. Today, it's more a question of looks, rather than lifestyle.

And if the punk style has made the pages of Scholastic magazine, how harmful can the trend be?