IF YOU LIVE in Silver Spring you can do all your Christmas shopping at Tyson's Corner and no one will stop you on the Maryland side of the Cabin John Bridge and confiscate the sweaters, stereos and Cabbage Patch dolls you have bought. The Constitution forbids interference with interstate commerce that makes it possible for merchants over the state line to compete for your business. But if you're going to have a New Year's Eve party at your home in Alexandria, you can't buy booze at a discount liquor store in the District because the state of Virginia won't allow you to bring more than a gallon of alcohol across its borders.

The distinction between alcohol and just about any other consumer commodity is specifically authorized in the 21st Amendment to the Constitution, which repealed Prohibition. Drafters wanted each state to be free to decide whether to allow liquor sales or to remain dry, or to adopt Sunday laws or liquor-by-the-drink rules or any other form of control. The amendment thus gives the states power to regulate the importation, delivery or use of intoxicating beverages, and they all do. Every state taxes liquor heavily, and that's what the current fight between the District and its Maryland and Virginia neighbors is all about.

Merchants in the city quite naturally want to be able to sell to out-of-state customers, but the states, equally understandably, don't want to take the revenue loss. Virginia officials, for example, estimate that they lose $14 million a year in taxes and profits because of sales in the District. But Washington likes getting those taxes too, so every year at holiday time the city thinks up a new way to thwart the Maryland and Virginia law enforcers who watch sales in the city. Out-of-state agents must obtain permits for surveillance. Last year they were required to give 30 days' notice of any activity, and this year the D.C. Council passed an emergency law banning the stakeouts entirely. Last week, U.S. District Judge Thomas P. Jackson refused to grant a temporary restraining order suspending the new city law -- a full hearing will be held later -- but he has the right idea on what should have been done by wise lawmakers. He found that both the equities and the public interest lie with the states, and he urged the three jurisdictions to cooperate with each other in enforcing legitimate revenue laws.

There are far more important questions that must be settled amicably in this region -- from Metro financing to sewage treatment. Nit-picking District harassment on liquor law enforcement only jeopardizes the cooperation among area jurisdictions that is needed every day, year in and year out.