THERE'S BEEN GOOD reason to breathe more easily around town. Over the summer the air was definitely not as dirty as it has been in the past. Not until Sept. 11, in fact, did the pollution index reach what is termed the unhealthful range, hitting a 110 reading at the Council of Governments station in Bethesda. There were several contributing factors, not the least of which was the weather. Though considered foul by many sun-worshipping standards, it was fair to ears, noses and throats. Those troublesome air "inversions" just didn't materialize. But it just may be that people did some constructive things that improved their air.

The Council of Governments did change the standards of air pollution "alerts" this year to conform with new federal guidelines. Until this year, index readings above 100 would trigger an alert. Now those are labeled "unhealthful" and they prompt a "health advisory." But the improvement in the air this year was not a numbers game. It was genuine.

What interests some transportation officials and environmental students, though, is the possibility that increased use of Metro may have helped. ThereS no direct cause-and-effect gauge, but gasoline problems certainly sent many area motorists scrambling to public transportation. U.S. Department of Transportation figures for toll roads around the region indicate significant decreases in vehicle miles traveled this year. And subway ridership, spurred by more miles of track, rose even more dramatically than Metro officials had expected.

Next year, of course, the subways may be more packed than ever -- and the air fouler than ever as well. But auto emissions do affect the pollution levels and, if relative relief is what residents seek, those who do abandon their cars in favor of buses and subways will be on the right track.