PERSNICKETY BARTENDERS almost anywhere in the world still refuse on principle to mix certain drinks they don't admire, but when it comes to serving beer to a 19-year-old in Alexandria, rights of refusal have been limited -- even through Old Town and younger townies haven't mixed at all well in the local taverns and restaurants. But with a 4-to-3 vote the other night, the city council found a messey way to mix up its drinking rules with voluntary prohibitions of beer sales to anyone 18 to 21.

Restaurateurs and barkeeps in this neighborhood first imposed the ban after complaints that the area had become the late-night playground of raucous young people -- even though Virginia law currently allows people 18 or over to buy beer. This resulted in a ruling by the Alexandria Human Rights Commission that a restaurant had violated a 19-yeard-old patron's rights when it refused to serve her a beer.

The agency said in effect that, under a city discrimination ordinance, at any restaurant or tavern, if you've got the legal age, you've got the beer -- because refusal of service to anyone 18 or over should be based solely on grounds of intoxication, improper dress or disorderly conduct. None of these circumstances was in dispute, nor did any party to the event allege that the 19-year-old had posed any such threat.

But enter the city council, with its vote to amend the human rights ordinance and allow the voluntary bans. It is a bad way to regulate. The council is giving its official blessing to unofficial voluntary, arbitrary across-the-board bans on beer sales to people of certain ages who are otherwise legally qualified in the eyes of the state to be served. What if neighbors in some part of town decided that middle-aged businessmen -- but not their female contemporaries -- were misbehaving too much after hoisting a few? Would a ban on sales to that group hold up for more than a round of drafts?

If the drinking age needs changing, those who seek a change should tell it to the state lawmakers in Richmond, from whom all beer-law blessings flow. And if things get rowdy in the meantime, the neighbors might seek enforcement of the existing laws on disorderly drinkers of any age, which surely were put on the books with just this sort of situation in mind.