If you've been around for a while, you know that sporadic crackdowns on traffic violators are of little value.

For a few weeks, motorists become a little more cooperative in obeying what ever law is being singled out for attention at the moment. Then the police shift their attention to other matters, and violations go right back up to the previous level.

So motorists can be forgiven if they were unimpressed with the recent announcement by Deputy Chief Ernest J. Prete that his Traffic Division intends to crack down on motorists who block intersections. The law says that if you can't clear an intersection before the lights change, you shouldn't enter it, and sensible drivers understand the need for such a regulation. However, the law is violated a thousand times during every rush hour, and as a result every vehicle on the street is delayed.

This column has for decades called for better enforcement of all traffic regulations, and has often singled out the blocked-intersection law for special attention. But several of our police chiefs have had little enthusiasm for having their officers "waste" time on traffic work, and during Jerry Wilson's tenure as chief, enforcement was particularly lax.

However, I am now getting a new set of vibes out of headquaters. Police Chief Maurice J. Cullinane seems to be giving traffic control a higher priority than Wilson did, and Prete's crackdown on blocked intersections may therefore have more substance to it than the fleeting campaigns of the past. If you are a scofflaw driver, you'd better keep a wary eye on developments.

If Cullinane really means to make traffic enforcement an important and ongoing function of the Metropolitan Police Department and if the traffic court judges co-operate with him, it could be a whole new ball game. We'll have to reserve judgment until the new attitude at headquaters is better defined.