YOU DON'T HAVE to go beyond the neighborhood fast-food chain or ice cream parlor nowadays to observe a phenomenon of far-reaching consequences: More high school kids are working longer hours and making more money than ever in our history.

At first glance, that may seem like an unqualified blessing. The work ethic lives. The kids are learning what it's like to make a buck. But a more careful look also raises some troubling questions about the way these young people -- especially middle-class youth -- are growing up.

What does it say about American priorities when kids spend more time working for big corporations and less time for their teachers? What happens to family life when jobs increasingly draw youngsters away from the home? How much authority or influence can parents hope to exercise over children who enjoy a degree of financial independence undreamed of 25 years ago?

A recent study by the Reagan administration's Justice Department attracted attention to another issue on the list: Is after-school and summer work related to juvenile delinquency? The department found that teen- agers who did work after school and on summer breaks had somewhat more run-ins with the police and were involved in more serious offenses than those who didn't.

But that only raises a further question: Given the mixed evidence, why has the Labor Department proposed revisions in child labor laws that would let 14- and 15-year-olds work longer, and later, during the school week? That proposal certainly doesn't follow the Reagan administration's rhetoric about how it wants to strengthen the American family.

Finally, what are all those kids out there working for anyway? The majority of them are not poor; they are white and middle class. They spend, rather than save, the bulk of the half-billion dollars they earn every week. Does this foreshadow a drift toward a still more materialistic America?

Whatever the answers to these questions, one thing is certain: The high school workaholic is a uniquely American type. In no other major industrial country are school children a prominent part of the work force. European, Japanese and Russian teen-agers study, participate in sports clubs and "hang out" rather than toil.

In America, though, at least a third of high school students hold part-time jobs in any given week. Of the 30.5 million kids between 12 and 19 years old, 18.6 million are employed some of the time, and about a quarter earn more than $200 a month, according to a study done last year by Simmons Market Research Bureau of New York. Nearly half the young men put in more than 20 hours a week -- the equivalent of all-day Saturday and Sunday and an hour a day after school.

This is no sudden trend; the portion of working teen-agers has been increasing steadily since 1964. A 16-year-old male attending school is five times more likely to work part- time than in 1940, and a girl the same age is 16 times more likely to work.

The statistics, in fact, point to a two-decade development rivaling in significance the rise of the working mother and chiefly involving white, middle-class youth.

The U.S. economy added 20 million jobs in the 1970s, of which some 7 million were low- paying, unskilled slots in retail businesses and "eating and drinking establishments." Most of those jobs were created not in inner cities, where youth unemployment is highest, but in suburbs, residential areas and towns where middle-class kids congregate.

When Ohio State surveyed a representative sample of 12,686 teen-agers for the federal government in 1979, it found that half of the whites attending high school were working, compared with only 27 per cent of the blacks. Among all the kids sampled, 62 percent of those who were not living in poverty were working, compared with 38 percent of those who were poor.

Labor Department statistics tend to bear out these surveys. While employment rates for blacks aged 16 to 19 have stayed fairly constant since the late 1960s, the rates for whites in this age bracket have shot up.

The new jobs were especially suited for these kids, and they swarmed into them -- and out of them -- at a dizzying pace. At any given time about 1.5 million teen-agers are employed by fast-food chains. A senior official of one such chain estimates that by the year 2000, 80 percent of all young people under 21 will have worked in a fast-food establishment.

Given the economic and social dimensions of the teen-age work trend, information about its impact on educational performance, families and teen-age attitudes is surprisingly scanty. But the evidence that is becoming available already has raised warning signals.

Nobody suggests that work is all bad for teen-agers. It does teach the value of money, provide a transition to the adult world, and keep kids off the street at a time when both parents spend less time at home. But how much work, and for what purposes?

Many kids from strong, stable families no doubt can handle the extra pressures, the financial independence, the need to juggle schedules and complete homework. But what of other adolescents?

Some of the most disturbing data has been collected by two social scientists at the University of California in Irvine, Ellen Greenberger and Laurence D. Steinberg. They interviewed 531 carefully selected 10th and 11th graders in Orange County to compare working and non-working kids.

"Employment is associated with lower school involvement, diminished school performance, decreased school attendance, increased cynicism about working, acceptance of certain unethical business practices, and increased alcohol and marijuana use," Steinberg subsequently wrote.

"We found that working long hours means less time on homework and decreased enjoyment of school," says Greenberger. "Working long hours is likely to precede a detachment from school, rather than to follow from that detachment. And of course it knocks out sports, extra-curricular activities or community service."

Among other things, Greenberger and Steinberg found that the students' grades dropped the longer hours they worked. Greenberger cautions that the research does not prove that work leads to bad grades; it may be that a poor student is predisposed to spending more time on a job than on homework. But the finding does suggest reason for concern and further study.

As for what kids "learn" on the job, in most cases, Steinberg maintains, the skills of communication, courtesy, and punctuality can be acquired in a few weeks. After that, the "learning curve" drops off to near zero.

Greenberger believes that the work explosion among middle-class teen-agers is part of a broad devaluation of education in America. According to this view, as schools have become less demanding, there has been more time for jobs. Moreover, as college educations have become available to virtually any teen- ager whose family can afford one -- regardless of high school achievement -- concerns of high schoolers about spreading themselves too thin may have declined.

The question, of course, is what the kids are doing with all their money? Anybody who thinks they're salting it away for future educations or helping pay the family bills should talk to some corporate marketing people, who know better. The kids are virtually supporting major sectors of the U.S. economy. The record business, the fashion industry, and dozens of other enterprises now tap the pool of loose change in teen-agers' pockets -- which is quite a bit of change.

According to Simmons' 1981 research, 7 million teen-agers earn more than $50 a week, while 5.8 million earn $10 to $49 a week and some 5 million make under $10. All in all, the earnings come to something like $500 million weekly, or $25 billion a year. Allowances add at least $2.5 billion more annually to cash in teen-agers' hands.

When Steinberg and Greenberger asked the kids they studied why they were working, the overwhelming majority said it was to earn money they intended to spend immediately. Only 2 or 3 percent were saving for a future education, and few were making a direct contribution to family finances (although many made an indirect contribution by buying their own clothes, meals or items that parents otherwise would have purchased).

This pattern of work and spending has resulted in what the University of Michigan's Jerald G. Bachman calls "premature affluence." When the value of free meals, free room, access to the family car, and family vacations is added to the earned cash in teenagers pockets, the sum becomes even more substantial.

Yet this sense of affluence is misleading, even unreal. Living in these conditions, teen- agers are denied the opportunity to discover the hardships of achieving real material independence, and the later transition to adulthood may therefore actually be complicated by the experience of working in high school.

Consider Charlie, a 16-year-old from Gainesville, Fla., who spent several hundred dollars of the money he earned at a Burger King last year on a diamond necklace for his girlfriend. Or take another teen-ager, employed at a Washington department store weekends and after school, who spends a good portion of her hard-earned cash on less durable commodities: marijuana and quaaludes.

A relationship between teen-age work and drug abuse, if not actual crime, actually had been documented before the recent Justice Department study stirred a flurry of editorial comments. The University of Michigan's Institute for Social Research, which does an exhaustive annual survey of high school seniors, has long reported that above-average alcohol, cigarette and drugs use occurs among seniors with heavy job commitments.

The latest Michigan survey found that only 20 per cent of the seniors reporting low weekly income said they had used marijuana in the previous 30 days. But the figure reached almost 40 per cent for those who reported high weekly incomes. Why? The availability of ready cash, stress and other factors have all been suggested to explain the phenomenon, but this is still guesswork.

The money in teen-age hands also creates tensions in families, as most parents can attest. While parents are relieved that children have a job and are paying for some of their needs, the financial independence of the children also loosens the authority of parents. Kids claim that parents have no right to interfere in financial decisions -- and parents often go along.

Greenberger suggests that the time may have come for parents to adopt a different policy, establish alternative values and help kids stave off the material pressures on them. "Rather than lay all the blame on these 'dreadful, materialistic teen-agers,' why not ask parents to exercise some restraints?" she asks.

Given the trends, however, that would not be easy. Some suggest it may have to be schools and families that adjust to working teen-agers, rather than the other way around. They say schools should face up to the realities of working students, help these kids identify what is educational in their jobs and what isn't, and generally work to establish a sense of perspective.

"The social norm in high school now is that you work," says Michael Borus, director of the Center for Human Resources at Ohio State University. "In my opinion, this represents to some extent a change in the social values of the kids. They want money to get independence. But their working may in itself be a function of other changes -- their school work doesn't take up all their time, and the whole family is work-oriented now. Mom is out working, and there's nobody around the house to talk to anymore. Instead of hanging out on the corner, you go down to the job at Baskin-Robbins. It isn't necessarily a negative development."