WHEN liquor companies look at American teenagers, they see dollar signs and a new generation of customers. Although the legal drinking age is 21, underage drinkers are estimated to consume more than 1 billion cans of beer a year.As one way of curbing youthful drinking, Surgeon General Antonio Novello wants beer and wine companies to stop "unabashedly" appealing to young people in their ads. She points to commercials that feature bikini-clad women, rap and rock music, and cartoons, charging that these "lifestyle" ads equate drinking with being "cool" and "macho." Liquor manufacturers, like cigarette companies, argue that advertising doesn't cause people to drink or smoke, but merely encourages them to switch brands. Yet if brand-switching was truly their only motive, would alcohol marketers' $2 billion advertising budget last year have been targeted so conspicuously at young people? Dr. Novello deserves praise for taking on the beer and liquor industries. Yet asking for voluntary compliance is unrealistic. Industry representatives say they will not ban any advertising. Just as cigarette packages and ads now carry warning labels, so should alcoholic beverages and ads. A bill before Congress would require liquor ads to carry one of five warnings about the dangers of alcohol. But curbing advertising is only one solution. Parents can play a part by helping to prevent unsupervised teenage parties, where beer flows freely. Indeed, the verb "party" is synonymous with drinking in the teenage lexicon. Adults tempted to feel relieved that their offspring "only" drink rather than use drugs must remember that the bottle, the can, and the keg remain dangerous attractions. In 1989 alone, alcohol-related accidents claimed the lives of 2,800 teens. The adolescent yearning to be accepted by peers runs deep. Dr. Novello describes the way this teenage vulnerability is played upon by liquor manufacturers: "The ads have youth believing that instead of getting up early, exercising, going to school, playing a sport, or learning to be a team player, all they have to do to fit in is learn to drink the right alcoholic beverage." Parents as well as peers must accept the responsibility of serving as role models.