PERHAPS A MILLION Americans will be flying or riding in aircraft today. Seventy-five years ago there was one. Actually there were two; after Orville Wright had made the first successful powered flight, his brother William also took a spin. If those bicycle makers from Dayton had crashed that day, no doubt they or somebody else would have gotten into the air eventually; manhs itch ot defy gravity is that strong. But the Wright brothers made it first. And so, about 10:35 this morning, air travelers the world around may pause to thank the men who enabled them to be wherever they are - grounded on standby or 30,000 feet up in the wild blue.

The diamond anniversary of powered flight is being marked this weekend with great bursts of soaring oratory and enough special programs and exhibits to satiate the most fervent aviation buff. Most of these flights of celebration are bound to emphasize the basic ways that aviation has transformed the world by bringing people closer together, enlarging our horizons, propelling mankind toward the moon and stars and - for some - giving new dimensions to the concept of fear.

But that is not the whole of the Wright brothers' legacy. Without airplanes, for instance, we would have a greaterr gasoline crisis, much more air pollution and even worse traffic jams, with no spotters in helicopters to tell us where not to drive. Without airplanes, King Kong would still be on the Empire State Building. No one have have gone flying down to Rio or come in on a wing and prayer. The careers of Van Johnson, John Wayne and D. B. Cooper would never have gotten off the ground. We would lack sky-diving, crop-dusting, holding patterns, sonic booms, jet lag, jet sets and shuttle diplomacy. Hawaii would be a rumor. Air mail would never have been.

Aviation created barnstorming, coffee-tea-or-milk and the small-tray industry. It has immortalized not only Eddie Rickenbacker, Charles Lindberg and Amelia Earhart, but also LaGuardia, Dulles and O'Hare. And all of this is ours because of individual initiative and the pioneering gumption of couple of nobodies from middle America. They didn't even have a federal grant.

How very fitting, then, that this country has already marked this anniversary by freein air travel from the bonds of regulation. Because of this historic step, flying is finally coming within the economic reach of average citizens. One result, we note ruefully, has been to clog the airports and turn great flocks of the Wright brothers' spiritual heirs into tightly bunched, intricately ticketed, carefully inspected and unintelligibly instructed sheep. But even that has its compensations. Think of them: breakfast in London, lunch in New York, dinner in Los Angeles and Luggage in Bombay.