AN UNUSUALLY large corps of midnight monitors will be manning duty posts on this special New Year's Eve, and still other erstwhile partygoers will stay put just this once, just because. But those who do choose to mingle downtown should be aware that drinking alcohol or possessing open containers of alcohol on National Park Service property or city streets is illegal. Word is that testing police tolerance on this point will prove unwise. With parking banned in large sections of downtown, Metro should be the way to go.

Tonight and throughout the holiday weekend, one of the greatest threats to survival will be the road-revelers: drivers with alcohol in their system. Totally polluted motorists are menacing enough, but they are outnumbered by deceptively dangerous drivers--those who feel sure they're "okay" but are not.

With sobriety checkpoints likely anywhere--and police in no mood to go easy on impaired motorists--anyone mixing drinks and drives will be risking legal trouble as well as tragedy.

The stakes are likely to grow even more in the new year. Mothers Against Drunk Driving, credited by federal and state officials as instrumental in campaigns to curb drunk driving and underage drinking, will mark its 20th anniversary with a focus on "higher risk drivers." In addition to those with dangerously high blood alcohol content levels, this category includes everyone convicted of a drunk driving offense within five years of a prior drunk driving conviction, and anyone convicted of driving with a suspended license that was lifted as the result of a drunk-driving arrest.

Congress and state governments will be urged to toughen sanctions and to set illegal blood alcohol thresholds at .08 percent. Opponents of .08--primarily lobbyists for those who market alcoholic beverages--"like to camouflage their concern about profits by arguing that we ought to be focusing all our efforts on higher-risk drivers," says incoming MADD President Millie I. Webb. "This is not an either-or proposition." The majority of alcohol-related deaths involve first-time offenders.

The new year's holiday is often the most deadly drunk-driving period of the year. Over the past two new year's breaks, 63 percent of all highway deaths were alcohol-related. On an average day the figure is 38 percent. Both percentages ought to be brought down. On average each week, 308 people are killed in alcohol-related crashes, about the equivalent of two jetliner crashes.

MADD is not crusading against alcohol consumption. People will party. But those who take the drinks should let non-drinkers take the wheels.