He is white, white collar and well off. He earns about $30,000 a year and probably has a graduate degree. He eats meat, does not smoke and his resting pulse is 52 1/2 beats per minute.

He is the average runner. He could be anyone.He could be Jimmy Carter.

"Carter is the classic jogger of the 1970s, albeit somewhat older," said Paul Milvy, a runner and assistant professor of community medicine at Mount Sinai Medical School in New York.

"Runners are extremely professional. They are nine times as likely to be scientists, they are rich, they don't smoke, they are thin, and possibly compulsive about their sport."

Two weeks ago, Carter had to quit a 6.2-mile road race -- his first -- after four tough miles. Runners, who tend to sympathize with him at least on road races, say the episode merely makes him more average.

"It happens," said Bill Lewis, a New Yorker who ran his first marathon there last year. "After my first race, I stood there triumphant for 10 minutes and then fainted. Just because it happens to the president doesn't mean it is unusual."

Carter's travail raised serious questions about the effect of running on the nation's health and about how seriously runners take their sport.

A recent Yankelovich, Skelly and White, Inc. study showed that 40 million Americans run.That is one-sixth of the population, half the number of Americans who voted in 1976.

Many people in the running establishment believe the 40 million figure inflated. "The 40 million includes people who jog down the stairs in the morning," said Liz Elliot, president of the National Jogging Association.

Ken Young, director of the National Running Data Center in Tucson, estaimtes 10 million runners.

That figure represents at least nine million more runners than a decade ago. There were 126 starters in the first New York Marathon in 1970 (four loops around Central Park). The field has been limited to 14,000 this year, and the course will touch five boroughs.

Running has become so organized that the National Running Data Center can tell you what size T-shirts participants in a race will wear -- one-sixth small, one-third medium, one-third large, one-sixth extra large.

Another survey of the New York Marathon recorded the percentage of runners who wore glasses before they were 20.

After 90 weeks on the best-seller list, Jim Fixx's "The Complete Book of Running," has sold 750,000 hardback copies.

Running is no longer just a sport; it is a market. Corporate sponsorship for the "in" sport has been provided by the "in" drink, Perrier, as well as by such brewers as Anheuser-Busch, which put up some of the money for President Carter's race.

"They were giving out free beer at the finish line," said Washington's Jeff Darman, former president of the Road Runners Club of America. Major Industry

Running gear -- shoes, T-shirts, shorts, sweat suits -- has become a multimillion-dollar industry with such name runners as Bill Rodgers and Frank Shorter endorsing clothes.

In its first special shoe issue in 1967, Runner's World magazine rated 16 shoes. This year's issue will rate 178.

John Horan, editor of Sport Style magazine, guesstimates that $250 million in running shoes are sold each year and that 40 percent are bought by nonrunners (the trade calls it the "vanity" market).

Herman's Sporting Goods store on E Street NW sells $5,000 worth of running shoes each week.

Running has been good to small businesses. Three years ago, Hunt Barclay, "was out running one winter night and had a close encounter with a snowplow. He looked around for something to wear that would make him stand out and couldn't find anything," said John Gotjen, financial manager of the Jog-A-Lite company. The firm produces 50 items of "high visibility" clothing for runners, from luminescent headbands to vests (the best seller).

Barclay, who started out selling his products from his living room table, grosses $50,000 to $60,000 a month, according to Gotjen.

Running has been hyped and heralded as the sport that requires nothing and no one. One running writer has called it "the most democratic sport." You don't need a partner, a court, or even any skill, he contends.

George Sheehan, the running cardiologist, agreed: "Most of the guys you see out running have chicken bones," he said. "They're not good at anything else, which is what I am. I'm tone deaf and my pain threshold is at the level of a firm handshake."

Sheehan describes himself as an "elitist." He has company. Sixty percent of the participants in the 1978 New York Marathon had graduate degrees. Fifty-two percent of the members of the National Jogging Association earn $30,000 or more, and 11 percent earn $70,000 or more. D.C. Tops List

Running is largely an urban phenomenon. According to the National Running Data Center, the District of Columbia has more runners in relation to its population than any other area of the country. South Dakota, North Dakota and Arkansas are at the bottom of the scale.

Milvy, who did a demographic study of the participants in the 1977 New York Marathon, said, "there appears to be an inverse relationship between activity on the job and off it. The middle class, we push pencils all day, and are more physically active off the job.

"The middle class relaxes by the sweat of its brow."

Conversely, as Darman points out, "For a guy who works hard in a factory all day doing heavy manual labor, it's hard to come home and decide what he needs is to run an hour to relax."

Fred Lebow, president of the New York Road Runners Club, said when "the fireman, the postman, and the secretary start running, that's when the running boom will be in. Tennis stopped because it could never filter down to that level. The average worker can afford to run."

Bill Lewis, a black sportswriter who runs in New York's Central Park, said, "At first, I ran into only professionals. Now, I'm running into bank guards and cabbies."

Although there are no reliable national statistics on black runners, Milvy estimates that blacks made up only one to three percent of the runners in the New York Marathon last year.

Lewis said, "When I starter running in August 1977, I wouldn't be the only black in a race of 400; maybe there were one or two others. Now in a race that size, you see at least 10 or 20 or more.

"Sprinting seems to be a way out of the ghetto," he said. "It can literally be applied to other sports like baseball and football. But long-distance running is not a monetary way out of Harlem or Bed-Stuy (Bedford -Stuyvesant)." Women Join In

Lewis believes that "the proportion of blacks running is about the same as the proportion of middle class or black professionals."

Ron Sutton, a black sportscaster at WHUR, the radio station of Howard University, believes "that the number goes far beyond that." The actual number of black runners, he said, is not reflected in magazine subscription and race participation figures, where entry fees can be as much as $10.

Although women constitute a minority of runners (approximately one-fourth of the 35,000 members of the National Jogging Association are women), their number is growing. In 1975, there were 19 men for every woman who crossed the finish line at road races tabulated by the National Running Data Center. Last year, there were 10 men for every woman.

This has not gone unnoticed on Madison Avenue. Avon Products, Inc., Bonne Bell, Inc. and L'Eggs, a division of Hanes Corp., sponsor women's racing circuits.

Katherine Switzer, first woman to compete officially in the Boston Marathon (in 1967 she entered as K. Switzer and when her gender was discovered, race organizers tried to rip her number from her shirt and pull her out of the field), now organizes the Avon circuit. She believes that "man's participation in running will peak in two years. Woman's running is just the tip of the iceberg.

"Women are for the first time experiencing the sensation of self-contained accomplishment," she said. "It's something they can do with no support from anyone. Men have had this sense of accomplishment in Little League and varsity sports. Running is something they do to get in shape fast, not for the sense of accomplishment the way women do."

People run for a variety of reasons; to be thin, to be in, to be with next of kin. (Though one Georgetown runner says he and his wife do not run together "for the sake of the children.")

Sheehan, who some think of as a running guru, said, "the evangelists who promote it (running) for lowering cholesterol and reducing heart attacks mainly make it tough for me." 'Life to Your Years'

He recalled attending a clinic on fitness where the first question directed at him, from a psychiatrist, was, "Will running prolong your life?" "I had had it up to there with that question, so I asked him, 'Will psychiatry?'"

Sheehan is fond of saying that "running will add life to your years, not years to your life." Many physicians, including President Carter's, Dr. William M. Lukash, believe the ancillary benefits of running promote longevity.

"Runners are losing weight, dropping blood pressure, lowering cholesterol, and if they're smokers, they'll tend to stop smoking," Lukash said. "So you've got a trend at eliminating the risk factors that we know without a doubt are associated with an increased risk of cardiac disease."

Those who run to live longer are doing it for the wrong reason, according to Dr. Samuel Fox, director of Georgetown's cardiology exercise program.

He said there is no long-term study proving that runners live longer. But there is some evidence that exercise might prevent heart attacks.

Fox takes issue with recently published reports of the prestigious Framingham Study labeling inactivity as only a "minor risk factor" for heart disease. Although he agrees with the study's findings that smoking and high blood pressure more dramatically endanger the heart, he said the Framingham study may underrate the benefits of exercise because Framingham (Mass.) residents are such a sedentary group.

In a more active population, sedentary men were found to have 50 to 70 percent more heart attacks than those who at least walked three miles a day, Fox said.

He said Stanford researcher Ralph S. Paffenbarger compared the health and exercise habits of 17,000 Harvard alumni, a much more active group than the Framingham residents. He found that any exercise seemed to protect against heart attack. Runner-Death Study

Although the benefit was greatest in those who used up more than 2,000 calories a week exercising (jogging a mile burns 120 calories), Fox said even an increase in activity from 500 to 1,000 calories weekly -- the equivalent of walking five extra miles a week -- reduced the chances of heart attack.

Every year, a few runners die of heart attacks. While the annual number of running-related deaths is not known, such deaths are likely to increase as more people run. So far, doctors have no reliable way to predict who is in danger.

Stanford researchers checked the medical histories of 18 people who died during or just after running, looking for clues that might have warned the runners and their doctors.

Their study, published in the journal of the American Medical Association, found that 13 of the victims died of hidden, advanced heart disease, with signs in several cases of recent blockage in a blood vessel. But only six of the 13 had a history of any heart or blood pressure problems, and the group had no striking risk factors that labeled them as victims, said Dr. Paul D. Thompson, a Brown University cardiologist who headed the study while at Stanford.

Thompson, who ran 16th in the 1976 Boston Marathon, said he pinpointed one clue which may have contributed to some of the deaths. Six of the 13 heart attack victims had developed new symptoms, such as chest or stomach pains, yet none had cut down on his running.

He said that runners dismiss such warning signs quicker than other people do, naively assuming they are immune to heart disease. Although usually health-conscious with regard to smoking and weight control, they "aren't as careful" to pay attention to pain during exercise, he said.

The runners who died ranged from new joggers to marathon runners. Three had had normal exercise stress tests (electrocardiograms taken with the subject on a treadmill), underscoring the difficulty of predicting who may die while running. Stress Test

Doctors face such "false negative" results no matter how they evaluate a patient's readiness to take up a sport.They advise a patient starting an exercise program to take into account family history, age, physical fitness, blood pressure, smoking and obesity. The cardiologists interviewed said they consider an exercise stress test, which costs about $150, a reasonable precaution for any man over age 40 about to start an exercise program.

A woman under 50 who feels well probably does not need a stress test before beginning to jog, said Dr. David Pearle, a Georgetown University cardiologist, though other physicians say women over 35 should be stress tested. But even patients under 40 should have one if they have chest pain or other exercise-related symptoms such as stomach pain, irregular heartbeat or extreme exhaustion, he said.

A 37-year-old marathon runner, Pearle said he had a stress test recently because of chest pain during training. Pearle discourages young runners without any symptoms from having the test because the chance of a "false positive" result in that group is high.

Dr. Edwin Dale, assistant professor of obstetrics and gynecology at Emory University Medical School, believes that "the effect of running on women's health is still the major problem in running."

Several recent studies suggest that long-distance running might cause amenorrhea, the abnormal cessation of menstruation. Last year, Dale studied women who ran more than 30 miles each week, casual runners, joggers and nonrunners. He found that 24 percent of the long-distance runners had zero to five periods each year (the casual runners had no problem).

Doctors have speculated that the interruption of the normal cycle may be related to the low levels of body fat in long-distance runners. Dale concluded that, "some of the women in our study had problems because of fat loss, others because of the (birth control) pill and still others because of the stress of training and competition.

"What's most important," he said, "is that the normal reproductive system is not destroyed. Rather it is resting. If they discontinue training and gain weight, normal menses can resume." Rule of Thumb

Dale and others are now studying pregnant runners. Dr. Charles Greenhouse has treated more than 75 in his Silver Spring gynecological practice.

According to Greenhouse, pregnant women can continue whatever they have been doing, but should not try anything new.

"It is not a time to up your mileage or improve your times," he said.

"Don't jog any faster than you can talk," he added. "If you are exercising aerobically, that is taking in as much oxygen as you are giving out, then the baby won't suffer from deoxygenation."

The standard rule is that if you can't carry on a conversation, you are probably running too fast.

Ken Young, director of the National Running Data Center, knows more, statistically, about running than just about anyone in the country.

"For several years," he said, "we've been waiting for it (the running boom) to level off. It does seem that a lot of people are dropping out. But the gross numbers won't change because you'll always have the beginning runners starting."

Young expects the "gross number" of runners to level off in 1980-81. "By then," he said, "the number coming in should be equal the number getting out."

All sorts of claims have been made in the name of running: Runners live longer, and love longer, as the T-shirts say . . . Running prevents heart attacks and could have prevented Watergate.

Darman, who believes it is a good enough reason merely to like to run, said, "In 1972, I was running with Egil (Bud) Krough (a former Nixon aide). I was working for McGovern while he was organizing the Plumbers. He was a pretty good runner. But it didn't change a thing."

Milvy, editor of "The Long Distance Runner, a Definitive Study," said, "You can think of running as a nice liberated thing or as a reactionary movement." He is not sure which.

"In the 1960s, we worried about trying to change things on a social basis, like racism. Today, we worry about changing ourselves. "it's the Me Generation." The peace marchers of the 1960s are the joggers of the 1970s.

Milvy, a runner, was disturbed to find that cocktail-party conversation last spring in running circles was more involved with mileage than with Three Mile Island.

"We jog while Rome burns," he said.