A COUPLE OF years ago a suburban family gave a party for teen-agers at which beer was not only provided to the guests but sold. Kids were required to pay for tickets, which were traded for brew. No one defended those parents or condoned that kind of arrangement for underage drinkers. Occasionally, too, teen-age parties get out of hand. Sometimes parents are away and kids run riot. It has been known to happen that 50 people are invited and 150 show up. Once in a while the host calls the police; usually it's the neighbors who do so. And if the party is disorderly, destructive or dangerous to the peace of the community, we all expect the police to step in.

But keep in mind that the party given recently by the Morgan family of Fairfax to celebrate their son's graduation from high school was different from any of these situations. The Morgans did not sell or provide beer to minors. In fact they went out of their way to discourage the consumption of alcohol at the party. They had enlisted a number of other adults to help chaperone, and while there was certainly a large crowd at the gathering, not a single neighbor complained to the police about noise or disorder. The police had even been notified of the party in advance by the Morgans, who seem to have been determined to do everything right.

Fairfax County Commonwealth's Attorney Robert Horan says there will be prosecutions in this case. But remember, no one has been charged with drunk driving, destruction of property or being part of some kind of uncontrolled mob. We'd like to know more about the charges that have been brought and whether the people involved have been treated fairly.

How common is it, for example, for police to enter private property uninvited to look for law violations? How many people know that they can be charged with "aiding and abetting the consumption of alcohol by a minor" if a 20-year-old sneaks a can of beer onto the premises? Are these kinds of prosecutions common? Is it the usual practice of Fairfax County police to give sobriety checks and blood alcohol tests to middle-aged women walking a block or two from home, causing no disturbance and accompanied by friends and family? Is it customary to arrest such a person, handcuff her and force her to spend the night in jail? Do the police frequently arrest passengers in cars where the driver is cold sober? At what point does a party given in a private home become a public event that the police can infiltrate?

Most of the people who are second-guessing the Morgans in this case grew up in an era when 18-year-olds could drink beer. Even today, some young people who managed to be "grandfathered", can continue to drink even though they are not 21. The idea that parents can entirely control the behavior of college-age kids at a private party -- one observer suggested organized games in the back yard -- is ludicrous.

The law is is also terribly confusing not only for the Morgans but for all parents of teen-agers who want to celebrate special occasions such as high school graduations and who do their best to see that parties are orderly. Mr. Horan must step forward and explain not only the charges and the police practices involved in the Morgan case, but the general rules that apply in the county for parties.

If the liability on parents who open their home to teen-agers is as great as it appears to be, Mr. Horan might offer a few suggestions on where teen-agers can go for a good time when all the homes of their friends and neighbors are closed to parties