Air conditioning has transformed American life.

WASHINGTON _ What 20th-century invention has totally transformed the way we work, play and live?

``The computer, no doubt,'' answers 25-year-old Elliot Forest, a graduate student at Howard University here. ``With the Internet and all that stuff, oh yeah, the computer.''

Wrong.

While computers, automobiles or even cell phones might seem obvious choices, one technological marvel has been even more sweeping in its impact on our culture in this century. It's the ubiquitous air conditioner. In fact, there wouldn't even be computers without air conditioning.

Whole densely populated regions of the country, including Washington, which was classified as a subtropical duty station by the British foreign service in the 1930s, would be barely inhabitable …