JOINING a virgins' club in high school would hardly seem to be the '90s path to popularity. But for a small band of teenage girls in Dallas, the unusual group symbolizes their commitment to their future.Corrian Spencer, the club's founder, was eager to avoid repeating her mother's experience as a teenage mother. With guidance from an innovative program for 12- to 17-year-old girls conducted by Girls Inc., Ms. Spencer is carving out a different life: She now attends college. At a time when casual sex has become almost a rite of passage for many teens, the three-year study by Girls Inc. (formerly Girls Clubs of America) offers encouraging news. Through mother-daughter workshops, educational and career planning, assertiveness training programs, and information about sexuality, the inexpensive program cut in half the proportion of 12- to 14-year-old girls who became sexually active. It also reduced by half the number of pregnancies among 15- to 17-year-olds. More than a million teenagers - 11 percent of all teenage girls in the United States - become pregnant each year. Nearly one-quarter will have a pregnancy by age 18, and 44 percent by age 20. Four of every 10 teen pregnancies end in abortion. The cost of government support to families formed by teenagers runs into billions of dollars a year. The cost in interrupted educations and careers is incalculable. Last month the 18-year-old star of the TV sitcom "Doogie Howser, M.D." complained that "being a virgin is driving me crazy." And so, in an episode that by all accounts was tastefully done, Doogie went to bed with his girlfriend, Wanda, taking care to use a condom. A few weeks earlier, Roseanne's daughter Becky announced that she was sexually active and needed birth-control pills. In the middle-class, make-believe world inhabited by Doogie and Becky, teenage sex carries a predictable glamour. Yet for poor teenagers in real life, the risk of sexually transmitted disease is assuming new dangers. The Centers for Disease Control found that between 1988 and 1990, the HIV infection rate doubled among young women. They are now one and a half times more likely than young men to carry the virus. Doctors fear teens may face a heterosexual epidemic. As one solution, however imperfect, teachers in 16 New York City high schools will soon begin distributing condoms upon request, without parental consent - a move that promises to raise legal and moral questions for years to come. The school board in Omaha, Neb., has voted to add a "contraceptive kit" to a 10th-grade human growth and development class. At the same time, the course will continue to stress abstinence. Abstinence has become a quaint and musty word. Like Doogie Howser, students often appear eager to shed what they perceive as the stigma of virginity. But now that the old problem of teenage pregnancy is compounded by the new specter of teenage AIDS, how much longer can parents and teachers pretend that superficial preventive efforts in schools will prove effective? Persuading people to alter their sexual behavior is never easy. Negative motivation - instilling fear of pregnancy and disease - serves as one approach. The more positive way of Girls' Inc. - teaching responsible decisionmaking, helping girls learn to say no without losing popularity - is another. At $116 a year per girl, the program represents a bargain. But neither the technical fix of contraception nor isolated cases of teenage idealism can begin to cope with the broad and deep confusions of the so-called sexual revolution. All the statistics add up to a conclusion as obvious as it is unfashionable: Decades of ever-expanding sexual freedom have produced something tragically close to the opposite of freedom in millions of damaged lives. How many more statistics are required before it will be conceded that nobody really won the sexual revolution?