IF EVER THERE WERE an effective way to focus the pie-eyes of drunken drivers on a sobering threat--namely, arrest on the spot--it is the Montgomery County police department's new practice of stopping traffic to check the alcoholic conditions of motorists. And if this practice can be carried out with the courtesy and good sense that seem to have prevailed during the first weeks of this program, it deserves the strong citizen support that it is enjoying so far--as an important effort to protect the lives of everyone using public roads.

That is a big if, we know, because anything that smacks of stop-and-frisk or discriminatory harassment by law enforcement authorities is subject to legitimate protest. But the drunk driver, like the loaded handgun-toter, is a potential killer on the loose, and every law-abiding citizen on the streets deserves not only effective police protection, but also reason to believe that the conditions under which drivers' licenses are issued are met by others behind the wheels.

Dry statistics--the routine radio readings of holiday death tolls on highways, for example--do not always hammer home the horror of drunken driving as the leading cause of highway deaths in this country. But then Montgomery County Police Capt. John Baker is one who knows--20 recent fatal accidents he investigated involved drunk drivers. Others who know painfully well are the relatives and friends of victims, starting with 110 people killed in the county between January 1980 and Oct. 30, 1981, when the program began, of whom a majority were in accidents involving drunk drivers. This statistic does not even include the five members of an upper Montgomery County family who were killed Thursday in an accident in Carroll County in which the driver of another car has been charged with driving while intoxicated.

The Montgomery County program, or any other like it, should avoid unnecessary harassment. For example, the teetotaling couple on the way to the theater should not be caught up in a huge traffic snarl on a main artery and then grilled unnecessarily for 30 minutes--or asked to get out of the car and do cartwheels at roadside. But reports so far indicate that the checking in Montgomery has been executed with courtesy and dispatch; everyone is stopped, but only when there are overt signs of alcohol use--evident odor of liquor, bottles or cans in the car, awkward movements or slurred speech--do the officers pursue any further questioning. No searches are supposed to be conducted; that policy should stick.

Should police have to wait until a car is weaving across oncoming lanes or barely missing pedestrians before chasing down or pulling over a car? Or isn't it better to get the message out to all that in Montgomery County, people who drink had best find people who don't to do the driving. complicated and unfair way of compensating members of Congress in the absence of a pay raise. The rewards are so uneven. It's far better, for example, to be a powerful Senate committee chairman commanding large fees for speeches and living with one's family in a $300,000 house in Wesley Heights than to be freshman congressman from New Jersey commuting home every night to see one's family and constituents. But as the midnight oil burned and the clock ran out, Congress decided that two flawed gifts were better than nothing at all. So it took the money and ran.