YOU MAY KNOW already -- because more and more Americans are finding out in the worst way -- what is the most frequently committed violent crime in the country today. It has killed more people in the United States in the past two years than were killed during the entire Vietnam War. The crime is drunk driving, and Congress has just acted to do something about it: legislation now before President Reagan for signature would establish incentives for states to crack down on drunk driving and would set up a computerized national driver register with information for state licensing agencies on whether a license has been suspended in other states.

No one on Capitol Hill is pretending that this measure would put a stop to alcohol-related car crashes, in which, if current rates hold, one out of every two Americans will be involved during his or her lifetime. But the bill's chief sponsors, Reps. Michael Barnes of Maryland and James J. Howard of New Jersey, have worked with experts and citizens' organizations to come up with inducements for a more coordinated law enforcement effort across the country.

States would be eligible to receive basic grants from the Highway Trust Fund by taking certain steps, including 1) setting a one-tenth of 1 percent blood-alcohol concentration as the legal definition of intoxication; 2) providing prompt suspension of a driver's license for at least 90 days on the first offense and one year on the second of anyone deemed to be driving intoxicated or who refuses a test to determine intoxication; 3) requiring a mandatory minimum sentence of 48 consecutive hours in jail or 10 days' community service for repeat offenses within a five-year period; and 4) increasing enforcement and education efforts in the states.

Research on drunk driving points to fear of arrest as the major deterrent. Experts point out, however, that crackdowns will only work effectively during the time of publicity. At that, officials of the Insurance Institute for Highway Safety have estimated that for every person arrested for drunk driving, as many as 2,000 others are drinking and driving without getting caught. Police checkpoints, when conducted properly, have helped on this score.

For Congressman Barnes, the tragedy and consequences of drunk driving came to light dramatically at a meeting two years ago with a little girl. Laura Lamb had, at the age of five months, suddenly become the country's youngest quadriplegic -- paralyzed for life from her shoulders down. Her mother organized Mothers Against Drunk Drivers in Maryland, which was instrumental in generating bipartisan support for the legislation.

When he created a special commission earlier this year, President Reagan noted that people are "outraged that such slaughter can take place on our highways. The mood of the nation is ripe to make headway." The bill before him is a significant response to this widespread concern, and deserves to become law.