FOR SHEER LEGAL variety, perhaps nothing tops the drinking laws of this country. From one town to another, there can be different stipulations as to age, day of the week and hour, posture while drinking, packaging of the beverage and proof therein. And yesterday, Maryland created yet another other special category of duly authorized drinkers: teen-agers who had turned 18 by Wednesday, and therefore are allowed to drink in the state under a grandfather clause in the new law raising the minimum age for anybody else to 21 as of July 1.

The purpose of this change, of course, is to curb drunk driving and auto fatalities; and if the law serves this purpose more than does serving the 18-to- 21 set, people are sure to say more power to it. But it may just be that tougher drunk-driving laws, along with stricter enforcement, would accomplish more than will this decision to redefine so sharply the eligibility of certain adults to exhibit adult behavior. If the correlation between drunk driving and age is the basis for raising the age limit, the minimum age probably should be 26 or 27--to cover what insurance companies consider the highest-risk age group.

There is another more serious potential danger stemming from the new law. Now, as they did years ago, the teen-through-20 crowd on the fringes of the District is likely to pile into their cars for a legal night on the city and then, after hours, try to drive home. At the beach, the refugee-drinker tide will be somewhat reversed: Delaware, with a drinking age of 20, no longer will be watching its young cruise over the state line to stock up in Maryland; 20-year- olds from Maryland will be going the other way to fill up. Up the road beyond Frederick, teen-agers who drive into, say, the race track at Charles Town also can legally toss down the beers at 18.

True, the District, West Virginia and everywhere else could raise their minimum drinking ages to 21 to match Maryland. Or perhaps all 50 states and the District might consider raising their minimum driving ages to 26 or more. Obviously, achieving any effective uniformity is unlikely. That is why the concentration should be on separating alcohol and driving at all ages. And on this score, both Maryland and Virginia have changed their laws for the better.

In Maryland, second offenders no longer may avoid convictions by receiving probation before judgment. Alcohol blood tests have become mandatory for any driver involved in a fatal car accident; and police may confiscate for 120 days the license plates of any repeat drunk driver. Also, Gov. Hughes reports that the state has received a $400,000 federal grant to pay overtime for state and local police who patrol highways where drunk driving has been most prevalent.

In Virginia, a second conviction will lead to an automatic 48 hours in jail; a third conviction will result in a minimum one month in jail and possible lifetime revocation of a driver's license. First offenders are no longer able to erase their convictions by entering rehabilitation programs.

Stiff sanctions, yes, but they are aimed correctly at the premise that drivers, no matter their ages, are courting disaster when they drink.