REGULATION OF PEOPLE'S activities in the wilderness may sound incongruous, but custodians of public resources have been driven to it, more and more, to keep fabulous, fragile areas from being trampled by crowds. In most cases park visitors are willing to cooperate in exchange for a richer, more peaceful park experience. Yet every new curb brings loud complaints - and so it is with National Park Service director William J. Whalen's decision to impose new limits on summer river-running in Grand Canyon and to phase out motorized rafts.

The traffic problems in Grand Canyon are quite new. Few people dared to run the wild Colorado River there until 1963, when it was tamed by the completion of the Glen Canyon Dam upstream. Then the rafting business surged. By 1973, over 15,000 people per year were taking the river-running-and-camping trips. The National Park Service had to set limits to curb pollution and protect the beaches, trails and historic sites. Even tighter rules on campfires and waste removal were imposed last year.

Restrictions that protect the wilderness are very justifiable, and much of the new plan, such as rationing summer trips, sounds good. But phasing out motors is somewhat different because they are being regarded almost entirely as polluters of the trip - as aesthetic intruders that mainly damage the visitor's experience. Outboard motors are noisy. They overwhelm quiet explanations of the scenery. They tend to be used for larger groups who often seem to be joy-riding instead of appreciating the uniqueness of the trip.

All those are purists' assertions, of course. Defenders of the motors claim that they are not that bad - and that restricting over 200 miles of the river to oar-powered craft will make the tours several days longer and somewhat more expensive. Yet given the time (at least a week) and cost (at least $600) that even a motorized trip entails, it's hard to see how barring motors will make a crucial difference. Most important, on the central aesthetic argument, Mr. Whalen is on the right side. The Grand Canyon is a very special place. No one will ever see it again in the purely wild state explored by Major John Wesley Powell's fabled expedition in 1869. But motors are an intrusion that add nothing valuable and take away a lot.