The smog that has been making life miserable for millions in this metropolis all summer long is a major factor in creating slums out of some once prime residential communities, according to a study being prepared for the Environmental Protection Agency.

Ralph D'Arge, an economics professor at the University of Wyoming, after over a year of work, is now completing a survey of communities here, which, he claims, shows conclusively that smog levels can determine whether a community becomes more or less affluent.

"In these really smoggy areas, you are getting a lower value for housing. People with money and a preference for clean air are moving out," says D'Arge, who expects to present his report to EPA in September. "You're getting poorer communities with increasingly more minorities. It really takes a toll."

One of the smog-infested areas studies by D'Arge is the San Gabriel Valley, a suburban area east of downtown Los Angeles that last year suffered more than 120 days of Stage 1 smog alert, meaning that young children and those with respiratory ailments were urged to avoid strenuous outdoor activity. This summer the valley's more than 1 million residents have been treated to a dozen more serious Stage 2 smog alerts in which even the healthiest individuals are urged to avoid breathing too much of the putrid air.

Smog, D'Arge maintains, has changed the life and character of such valley towns as El Monte, Alhambra and San Gabriel, which, virtually all middle class and white before the smog reached them in the 1960s, are quickly becoming dominated by poorer, mostly Mexican-American residents. A recent report by the Los Angeles Community Development Department cited the valley as one area changing dramatically from predominatly Anglo to Hispanic.

Donna Crippen, a 48-year-old native of El Monte, says the smog started pouring over the hills from Los Angeles on a regular basis a little more than a decade ago, changing forever the suburban community of 62,000. "You used to be able to go up in this alley and see Mount Baldy 50 miles away," she recalled. "Now you can't even see the stars at night because of the smog."

Before the smog came, Crippen, whose husband Jack is mayor, says El Monte was overwhelmingly a comfortable community of well-kept houses surrounded by walnut groves and fields of strawberries. Today, many once-substantial homes are rundown, littered with trash and scarred by graffiti, and the tide of Mexican-American immigration has risen to the point where Mexican Americans compose almost one-half of El Monte's population.

The EPA study, according to D'Arge, found similar negative effects on communities all along the Los Angeles "smog belt," stretching 40 miles east and downwind of downtown. At the same time, D'Arge adds, many once-deteriorated sections in less smoggy areas, particularly near the beaches, are experiencing an unprecedented boom in real estate.

Bob Lowes, a spokesman for the California Association of Realtors, agreed that there is no questionl that prices in "clean" areas are skyrocketing above those in residential areas once considered more fashionable but that now are blanketed by smog.

D'Arge found that people who can afford to are willing to spend, on the average, $2,000 a year extra to live in non-smoggy areas.

In the working-class Mar Vista area, in the "clean" west side of Los Angeles, for instance, prices for modest homes have risen in the past decade from $25,000 to more than $110,000, according to real estate agent Joe Viestra. The average price for a home in Upland, a suburban area deep in the "smog belt," today is $53,000, or half that in the "clem" areas, according to figures provided by Vernon Riphagen, president of the local realtors association.

"If you were to overlay a map of the areas which have been growing most rapidly with a pollution map, you'd find a very strong correlation," claims Tom Lieser, an economist for Security Pacific National Bank in Loe Angeles. "There is no doubt clean air is capitalized into property values."

Despite the smog and the statistics showing spreading barrio, or Mexican-American slum, conditions throughout the "smog belt," many realtors in areas with poor air quality believe their communities thrive even in the face of the snog. "People will live with it, they get used to it, it's like a toothache," Upland realtor Riphagen said.

But Prof. Ward Elliott, who teaches political science at Claremont University in the San Gabriel Valley, has studied the situation and concludes that property values are being kept down by the smog. "Of cource the realtors and the property owners have a vested interest in not admitting that their property values are affected by the smog, but the fact is they are," he says.

While they won't publicly admit concern, valley businessmen privately admit that the almost daily reports here ahout their area's air quality could be chasing away affluent residents and businesses. "They call the valley unhealthful on the radio and Santa Monica and the beaches healthy. Somebody hearsthat and you've got to admit it's not encouraging them to come to San Gabriel," one businessman said. "Nobody wants to admit it but there's no question it bothers one."