When Pam, Clair Huxtable's cousin and the newest member of "The Cosby Show's" revolving household, realizes her boyfriend wants something more than just "sugar," she dives into the perennial debate of whether to have sex.

The topic of tonight's special hour-long "Cosby," only the second expanded show in its history, is teen sex, couched in a dozen euphemisms but crackling with disarming peeks into teenagers' conversations and the ambivalence of everyone's helpful counsel. It airs on Channel 4 at 8.

The show takes on the issue in the same way it has been a bellwether on other social issues -- it is unafraid to temper or utilize its comedy for a message. The audience's interest will probably be heightened for several reasons: because Cosby has written bestsellers on parental travails, because teen sex and the epidemic of teenage pregnancies continue to be a crises for black and white families, and because those who need some guidance would probably be drawn more to the television solutions than a school-assembly lecture.

So how do the Huxtables handle the matter? Clair Huxtable, an attorney and mother of five, tries parable. Cliff, she recalls, told her one of the oldest lines ever, that sex would clear up his acne. Her dilemma was resolved with their marriage.

Cliff, the gynecologist and obstetrician and father of five, passes the buck. When Pam asks for a prescription for birth control bills, he tells her he will give her the name of another gynecologist if her mother approves.

And Clair tries some girl-to-girl prodding. "If a man is good, he will understand it is your decision," she says. They skip preaching: When Cliff gets a call from a 16-year-old going into labor, he comments on the awkwardness of the situation to Clair.

The show skillfully handles how this decision becomes a public matter -- right there on the basketball court at the community center -- the intensity of peer pressure and how important a decision about first sex can be to a teenager's fragile self-perception. But the script never has the boyfriend, Slide, asking Pam directly, "Will you go to bed." At one point, he says, "Let's get busy."

This is not bold but it is instructive. Some of the action is too real. After some goading from his friends -- "You are not a man unless you can handle your woman" -- Slide visits Pam just to have a discussion about sex. "It's time we took our relationship to another level," says Slide, arguing everyone else is doing it, how happy one of her girlfriends is now she is allegedly doing it. Pam is immediately suspicious about this approach. "That's a big step," she says. "I will be taking it with you" is the reply. Right there Pam needs the audience of advice from the "Go on Girl" segment of "In Living Color" shouting warnings about marriage papers, diapers, short-term lovers.

But the Cosby approach is proper and the direct and comic consciousness comes from a girlfriend who tilts back her head and shakes it and denies any intimacy with her boyfriend. "Let me just say what I have may not be precious to the world but it is precious to me. What I got is no knickknack." Like Clair, the friend also says the decision rests with the woman. "They got to listen to us," she says, and forget what their friends and hormones are saying.

Meanwhile the high school boys are debating where the women who will say yes live. One suggests Trenton, N.J. When Pam gets a supply of condoms, she shows them to Slide but at the same time tells him she wants to wait. Whether she does or not and how this social dilemma is solved will just have to be seen.