For years now University students have defied one of Cambridge's most arbitrary laws: the ban on all night parking. And, except for periodic spurts of activity by local policemen, they have escaped unticketed. But lately another crusade has commenced, and little remembrances from the local law enforcers bring the law back into gloomy prominence.

As protests pour in, the police present a series of rationalizations in answer. They carp on the old favorites of parked cars impeding snow clearance and blocking fire engines on the way to a night-time blaze. Now that snow has migrated north, the study fire engines must bear the bulk of the rather shaky argument. During the day the Fire Department has to battle through streets cluttered with parked and moving cars, and seems to fare pretty well. There is no reason why they could not do even better at night, when there are few drivers about.

But there is still one more argument tradition. Cambridge has lived under the law for so long that it has become an established part of the local color. Moreover, in the past few years, a new tradition has sprung up. A committee of the Cambridge legislature dedicated itself to the problem and has been playing it for two years. But the inactive past of this group foretells dim hopes for future action.

Of course, if they did stop toying, the committee could offer something more valuable than controversy. Instead of forcing residents to continue pocketing tickets, Cambridge could compromise tradition with sanity by allowing all night parking on one side of the street. Making one side so temptingly legal, the city might coerce the now defiant motorists to park single file in- stead of haphazardly blocking both sides. The Fire Department admits that with one side clear even the chubby hook-and-ladder could slither through the city.