Sweltering summer heat has returned, and with it the Washington wilt.

Seasoned observers of the wilt say it strikes people within three paces of their emergence from a car or building that is blessed with air conditioning. It takes that long for the full wallop of the hot, moist air to sink in. Then some people sag perceptibly at the knees, others glance toward the heavens in reproach and almost everybody utters some variation on the general theme of "ugh."

But wait. The lack of air conditioning didn't always mean disaster and the end of life as we know it. It didn't always herald the approach of doom, as many seemed ready to suggest with the onset of the kind of heat that gripped Washington and the East Coast yesterday, pushing the temperature at Reagan National Airport to a record-shattering 102 degrees. (And the forecast for today is just as bad.)

Time was when summer heat meant straw rugs, awnings and the gentle back-and-forth nod of an electric fan. It meant ice wagons and palm fans, sleeping outdoors at Hains Point in the District or on a tenement fire escape in New York.

It created "summer bachelors," fathers who stayed in town when the family left for the seashore. It brought the sound of the cicada through the windows by day and the call of the whippoorwill at night. There was a benign summer rhythm. Things slowed, relaxed, abated.

It wasn't the end of the world.

What happened?

Are we now wimps -- seduced by one of technology's grandest comforts -- where once we were in touch with our land, our climate and our sweaty selves?

Or is this a natural advance? "If man has the intelligence to heat his house in the winter time, why does he not cool it in the summer?" Alexander Graham Bell asked in 1914. Said someone else: "If they can cool dead hogs in Chicago," why not people "in the New York Stock Exchange?"

Whatever. Air conditioning has wrought a vast change, physical and psychological, across the land since the first home unit was installed in a Minneapolis mansion in 1914, and the first car unit -- a monstrosity mounted on the trunk -- went into a Houston businessman's Cadillac in 1930.

"Before air conditioning, people were much more tied to their everyday activities and routines by the weather," says Donald Albrecht, co-curator of an exhibit on the history of air conditioning at the National Building Museum in Washington.

"Now we can make nature conform to our desires," he says. "It seems to be, for better or worse, a characteristically American thing to do." Early ads for air conditioning, he notes, called it "man-made weather. They weren't just cooling you down, they were doing something elemental in nature."

The effect has been broad.

For one thing, air conditioning has kept politicians in Washington much longer than in the old days.

"I date the end of the old republic and the birth of the empire to the invention . . . of air conditioning," the novelist Gore Vidal wrote in 1982.

"Before air conditioning, Washington was deserted from mid-June to September," he wrote. Now, "Congress sits and sits while the presidents -- or at least their staffs -- never stop making mischief."

It enabled, with the now venerable air-conditioned theater, the summer blockbuster. Before air, historians have noted, theaters were even less hospitable than they are now.

Also possible now was the almost-as-venerable ranch house -- designed with air in mind, and nary a thought of cross ventilation. Buildings no longer had to be designed to help their inhabitants cope without air conditioning.

Nowadays, 76 percent of American homes have some form of air conditioning -- 48 percent with central air and 28 percent with one or more window units, according to the Arlington-based Air-Conditioning & Refrigeration Institute.

In the South, where some experts think air conditioning has affected everything from novel writing to the growth of cities, 94 percent of homes are now air conditioned, the institute says.

In 1970, the overall figure for central air was 10 percent -- which included the 1952 Fairfax County development of Valley Brook. Equipped with units powered by natural gas, the development is believed to be one of the first in the nation with central air.

Of the cars made in 1970, 4.8 million, or 60.9 percent, had factory-installed air conditioning, the institute says. In 1997, 6.7 million cars, or 95.7 percent, had factory air.

Everything seems to be air conditioned now: parking lot booths. Highway toll plazas. Even the Alamo.

Albrecht, the curator, says the growth of the industry has been just like the computer's, where "it's ugly and big and custom in the beginning, then it becomes smaller and miniature and less expensive, and it goes from an elite thing to an everyday thing."

But there has been a price.

"We've probably lost a sense of the natural rhythms of life, in a way," Albrecht says. "But it's not just air conditioning" that has wrought that change.

Lehigh University historian Gail Cooper, whose book "Air Conditioning America" was published last year, says the technology has brought a fundamental change in values.

Take the definition of fine weather.

"Before, a natural climate defined the ideal good weather," she says. "You would say, `As beautiful as a summer day at the beach' or `as a day in the mountains.' "

Now there is scientific talk of human "comfort zones" and how many comfortable days a city has a year. "It's not natural climate that is the standard anymore. It's kind of a scientifically designed ideal. It's pretty hard for any natural climate to stand up to that comparison."

All of this, though, would probably sound like hooey to the pioneers of cool who struggled during the 19th century and the early years of the 20th against the discomfort and disease that attended summer heat.

John Gorrie, for example, the Apalachicola, Fla., physician who in the mid-1800s tinkered with ice buckets hung from a hospital ceiling to ease the suffering of his malaria and yellow fever patients.

Or Willis Haviland Carrier, the New York engineer who devoted his life and his name to the industry, but who died in 1950 having missed out on the boom in home air conditioning his research helped create. His "atmospheric cabinet," a crude home unit, flopped in 1932.

Or Stuart W. Cramer, who in 1906 coined the term "air conditioning" to describe the yarn-saving dehumidifying process he used in North Carolina textile mills. Searching for a good term, he wrote, "I finally hit upon the compound word, `Air Conditioning,' which seems to have been a happy enough choice to have been generally adopted."

Indeed, air conditioning has been a boon to manufacturing, pharmaceuticals, medicine and food processing.

But its impact on people seems paramount.

"When you are cooled the heat becomes more unendurable; it becomes hotter and hotter outside as you get cooler and cooler inside," the architect Frank Lloyd Wright, an opponent of air conditioning, observed in 1954.

"I doubt that you can . . . make a climate of your own," he concluded, "and get away with it without harm to yourself."

Keeping America Cool

Seventy-six percent of all U.S. housing units are equipped with air conditioning. The technology of "engineered air" revolutionized the way Americans live, work and play.

1902: Willis Carrier builds the first air conditioner to combat humidity inside a printing company.

1906: Carrier patents his invention, calling it an "Apparatus for Treating Air." The term "Air Conditioning" is later used.

1922: Grauman's Metropolitan Theatre in Los Angeles becomes the first air-conditioned theater; by the late 1920s, most movie houses become a haven from summertime heat.

1928: The chamber of the U.S. House of Representatives becomes air-conditioned.

1929: The U.S. Senate chamber becomes air-conditioned.

1930: The White House, Executive Office Building and the Department of Commerce become air-conditioned.

1946: The demand for room air conditioners surges after World War II. Thirty-thousand of the units are produced this year.

1957: Air conditioners are redesigned, permitting units to be smaller, quieter, lighter and more efficient. A study conducted by the General Services Administration finds that productivity in government offices increases by 9.5 percent with air conditioning.

1970: Ten percent of U.S. homes have central air conditioning.

1996: A record 5.7 million units are produced; sales increase from the previous year after a summer of severe heat waves.

1998: More than 6 million air conditioner units produced.

SOURCES: Energy Information Administration; Air-Conditioning & Refrigeration Institute