BOSTON, Nov. 27 -- The November dance at Weston Middle School was canceled. Not due to weather or lack of interest or chaperones. It was canceled because of dirty dancing. Or, to be specific, "inappropriate body contact" at the October dance.

To be very specific, a group of 20 to 25 kids were bumping and grinding to the music. Some boys removed their shirts. Some girls unbuttoned or unzipped the tops of their hip-huggers. The children involved were 12 and 13 years old. Dances are huge here, and it was hard to cancel it, but we needed to make a statement that the recreation department was not going to allow this kind of behavior," says Diane Dinell of the Weston Recreation Department, which sponsored the dance.

Not so long ago, at Catholic school dances, nuns would move from couple of couple, warning them to leave enough room "for the Holy Ghost." Today, you couldn't squeeze a toothpick between some of the young couples on the dance floor.

And "dirty dancing" may be the least of parental nightmares. Though there are few hard numbers on the sexual habits of young teens, the incident in Weston, Mass. and other anecdotal evidence suggests that they are becoming more sexually precocious. Nowadays, puberty begins at a younger age--and so, apparently, does sexual experimentation.

A recent "sin poll" conducted by a student newspaper at Milton Academy found 15 percent of freshmen reported having engaged in oral sex, twice the number who said they'd had intercourse. After a dirty dancing experience a few years ago, Collins Middle School in Salem, Mass. went into "shutdown," and the entire school developed rules for proper behavior at future dances. In a manuscript psychologist Michael Thompson just completed on children and social cruelty, he cites a survey in which 25 percent of eighth-graders reported fondling another's genitals.

"The big thing in the eighth and ninth grade used to be kissing and touching, and now that is being fast-forwarded to having oral sex," says Catherine Steiner-Adair, a Lexington, Mass. psychologist who treats adolescents and adults. Her message to both boys and girls is simple: Wait. "A bad early sexual experience can really affect you later on in having good, healthy romantic relations."

The good news is that there has been a decrease in sexual intercourse among teenagers. According to a survey last year by the Kaiser Family Foundation, slightly less than half of high-school students had intercourse, down from 54 percent in 1991. But the other news is that more teenagers are engaging in oral sex: 55 percent, the same survey found. They reason that they can't get pregnant and think--erroneously--that they can't get AIDS.

Interviews reveal that many middle schoolers are following the high schoolers' lead. "People are pretty wary about having real sex," says one 13-year-old boy at a suburban school where an eighth-grade girl was recently discovered performing oral sex on a male classmate. With intercourse, he says, "a lot can go wrong. It can screw up your life." But the boy and his friends don't equate oral sex with actually having sex. "It's just hooking up," he says. "It happens all the time." And dirty dancing? "It's not like a sexy thing," says 14-year-old George Sholley of Milton. "It's just the way you dance."

In today's teen lingo, "hooking up" is the term of choice, and it can mean "anything from kissing to third base; it's not the home run," as the 13-year-old boy puts it.

Stacey Harris, a 12-year-old who attends Milton (Mass.) Academy, has seen couples making out at parties since early sixth grade. "There is peer pressure to hook up. You gotta know that just because you don't, people won't hate you," she says. "The guys who hook up are cool, but the girls are called sluts or ho's. There's no such thing as a guy slut."

Therapists who treat adolescents are hearing more and more from girls who feel coerced into substituting oral sex for intercourse. And in interviews, middle-school girls describe oral sex as a way of preserving their virginity. "It's totally different from real sex," says one 14-year-old who attends a private girls' school. "We don't call it sex. It's very common in the eighth grade. Girls do it to be cool, and to protect their reputations." It's okay to have oral sex at her age or younger, she says, but not sexual intercourse. "The worst thing that can happen to a girl is to get pregnant."

Two eighth-grade girls who attend a Dorchester middle school in Boston say that pressure from boys to perform oral sex starts in the seventh grade. "Boys will say, `Will you do me?' I say, `No way.' It's not worth the diseases," says one 13-year-old. Talk to the boys, however, and they deny any coercion. "We ask them, and if they say no, that's their choice," says one 14-year-old boy. He adds: "But sooner or later, they may say yes." His two friends nod in agreement.

Thompson, who has written several books on adolescents, tells of a seventh-grade boy who engaged in oral sex with an eighth-grade girl

. "He said to me, `I know this is supposed to be very exciting, but I haven't reached puberty yet.' "