Originally used to control moisture in a Brooklyn printing plant, air conditioning was first installed for the comfort of people in 1922, to cool the beated brows of those at Grauman's Chinese Theater in Hollywood.

It came here in 1924, to the Palace Theater, where air conditioning pampered an approving audience with a previously unknown amenity. Since then it has spread to 85 percent of the homes here - indeed, without air conditioning, the extraordinary population movement of recent years to the South and West would never have occurred.

Yet for 22 days this month, the machines that for decades have been thought of as a luxury have become the dividers between life and death. In the last few weeks, more than 20 people in America's 10th largest metropolis have succumbed to the effects of unrelenting 100-degree-plus temperatures and they had one thing in common: either by choice or by chance, they didn't have air-conditioning.

Almost all of them shared the fate of being too poor to afford an air conditioner and too old and infirm to live without one, according to the chief field agent of the Dallas County medical examiner's office. So the victims of this weather disaster have been culled from the ranks of the less well off while most of affluent Dallas has carried on in it's three-piece suits and high-collar dresses, taking time off from the glass towers to make the lunch-hour a picnic in the park.

These deaths - there are always a few such every year, but the current incidence is well above normal - have provided an intriguing insight into Dallas, nearby Fort Worth and the curiosty of the 1970s called the Sun Belt.

Air conditioning made the summer temperatures bearable to newcomers flocking to the economic opportunities of the desert cities like Phoenix of semi-tropical cities like Houston.

"Air conditioning has been a very great factor in the growth of Texas," says Sen. John G. Tower (R-Tex.) in looking at his state's emergence as the third most populous in the nation.

"They're too expensive," says the new widomer of Willie Davis as he sits on the sofa of his $40-a-month railroad flat house where Mrs. Davis, 50, was fatally overcome by heat and died Monday.

The retired highway construction laborer's windows are open and, so is the door, in an unsuccessful attempt at ventilation, and across the freeway from his ramshackle house is the towering skyline of the new Dallas, with its office buildings of sealed refrigerated refuges.

In west Dallas, the carton for a box fan - too little and too late - stands with other refuse in front of the tiny white frame home with red trim where the current heat waves' most horrible incident occurred.

Inside, Roy Hickman, 86, and his wife, Floyd, 76, both died of heat stroke complicated by their heart problems - almost at the same time.

In the Dallas Housing Authority complex on Lafayette Place, where Ruth Cotton, 68, lived until she was fatally stricken by heat on July 14, stoops and hula hoops have become the diversion from the temperatures. Most of the apartments there, like Cotton's, are among the few - 5 percent - of Dallas apartments lacking air conditioning.

So was the apartment of Otha Wright, 60, who was stricken last Saturday after suffering cramps after drinking a large amount of ice water. Her body temperture had reached 108 degrees before her death that night.

"Saturday evening it was just so miserable hot," said Wright's mother, Eula McCray. "She shook her head and said, I'm so hot," "And she passed out.

McCray, sitting amid the flowers and food sent over by friends after Wednesday's funeral services, said Wright just didn't like air conditioning. Two box fans stirred the air in their second floor walkup apartment.

This oppressive and prolonged heat began somewhat lark-like on the first of the month, as thousands of young people chilled themselves in ice tanks as they celebrated the Fourth of July weekend at a rock and roll and country music festival at the Cotton Bowl.

But then Dallas had 22 straight days of temperatures reaching 100 degrees - three days short of the record hot spell set in 1954. Thursday the temperature finally dipped to 99. The problem has not been extraordinarily high temperatures, just an unbroken string of days with above normal readings.

Too, there has been no rain for 42 days.

"We know when the lawn-mowing season starts we're going to have some "heart-related deaths, says Tarrant County (Fort Worth) medical investigator James Seaberry, "but this has really blown it out of proportion."

Seaberry says it has "absolutely" been the elderly and the poor who have been victims in Fort Worth.

The two younger people to die here in Dallas were working outdoors doing heavy labor, like Silverio Lopez, 35, who died of heat stroke after he collapsed at a construction site during his first day on the job.

For most middle-and upper-class Dallas residents, keeping cool has been no problem except for air conditioning failures. Repairman are running a week behind schedule and are working primarily on emergency cases.

But many residents, such as Mary Bowen, who lives in the projects of west Dallas, can only hope to wait out the summer in a cramped apartment, where she singlehandedly raises her eight children.

By day, they drink ice water and Kool-Aid, eat ice cream and take frequent showers. Although Bowen has three small box fans, they are not enough. "Sometimes," she says, the fans just blow hot air."

The problem is aggravated for the elderly who are afraid to leave their windows open at night. Says Anna Mae Crawford, 70, "I stay in my house by myself and I'm afraid to keep'em open." But for others, ventilation is worth risking crime. Says Jodie Bandy, a diabetic in her 70s: "I keep the windows open and run my box fan. I figure the Lord will take care of me somehow, someway."

But one unidentified man about 60 was apparently looked after neither by the Lord nor by the Dallas police. He was seen lying alongside some downtown railroad tracks and was pointed out to at least one officer by a passerby on July 13. Others also called the police, but he was still there, unconscious, the following morning.

Only then was he taken to the hospital, and last Sunday he died of heart stroke. A Dallas police department internal affairs investigation has been ordered.