IT IS FRIDAY, and if we may pass along a tip for all motorists before their offices go hollow for the long weekend, it is that the arm of the law will be longer than ever on the roads leading out of here today. We have this on good authority--in fact, authorities from police departments in all surrounding jurisdictions and Delaware were in town yesterday to report that they will be watching, stopping and arresting anyone they believe to be driving under the influence of too much alcohol.

Is this just another routine kill-joy holiday warning? Trouble is, too many people see it that way-- even though alcohol-related traffic accidents kill and maim people at an alarming rate. The most effective way to stop this violent killing, authorities believe, is to keep hounding everyone about this subject. And thanks to a new regional campaign, there are encouraging results. "Project Graduation" --with roadblocks, with warnings everywhere including formal-wear rentals, florists' boxes, table tops at prom dinners and the counters of liquor stores, and with dial-a-ride programs--was a definite success:

Greater Washington had no fatal accidents or serious alcohol-related accidents that could be tied to any graduation activities this year. And now this same attention is being focused on a "Safe Summer" program--seasonally adjusted, but delivering the same basic message. The challenge is to keep the attention level up, which is why local businesses, civic groups, governments and media contributed an estimated $98,500 in time, talent and other assistance to promote the graduation program.

Now that graduation's over, it would be good if those who have yet to graduate--as well as all their parents, friends, neighbors and fellow Americans-- could live through the summer. If drinkers let others be drivers, it could happen.