Rich Garcia, the son of a Mexican fruit picker turned foundry worker, remembers the days when his father drove him and his brothers down from East Los Angeles to watch the bullfights in Tijuana.

Pointing to Mexicans removing the droppings from the bulls and then to well-off Anglo-Americans drinking and having a good time in the best seats at the bullring, Rich Garcia's father said to him: "You can be like those people sweeping up after the bull or you can go to school and be like those people sitting in the good seats."

Twenty years later, Garcia is happy he needed his father's advice and acquired a college degree in public administration. He is assistant to Mayor Pete Wilson in San Diego, where Mexican-Americans have a city councilman of their own heritage for the first time in more than a century.

But though there are many such individual success stories, the majority of Mexican-Americans are still figuratively sweeping up after the bull.

Statistical data is scanty, largely because the Census Bureau classification of "Hispanic origin" yields little precise information about Mexican Americans. But the available evidence, including a 1976 Census Bureau survey that shows Hispanic-origin families with a median income of $10,000 compared to $15,200 for other families, suggests that Mexican-Americans are poorer, less-educated and much younger than other U.S. citizens. Forty-two percent of the Hispanic-orgin population is under 18, a harbinger of the day expected to come in the next decade when Hispanics will become the nation's largest minority group.

The face of the national future already is apparent in the Southwest where two realities - that the United States is a rich country and Mexico a poor one - are being blended into what some are referring to as a new nation - MexAmerica.

Two Hispanic economic communities flourish side by side in this regioN, united by an ancesteral heritage but separate by a gulf of citizenship. One is the community of U.S. citizens of Mexican ancestry, who occupy a disproportionate number of the bottom rungs of the economic ladder but are struggling to improve their living standards, education, job skills and political influence. The other is the community of the illegal immigrants, whom both Mexicans and Mexican-Americans prefer to call "undocumented workers."

The illegal immigrant occupies a shadow world of fieldhands, bus boys and day laborers working, at $2 an hour or less, for employers who do not speak his or her language in jobs that most native Americans are unwilling to perform. Usually, the illegal immigrant has suffered risks and indignities to acquire these menial jobs, which pay from three to six times a day what the individual would be making in Mexico.

Fear of deportation prevents protest of even the most unfair treatment or the least safe working conditions. the illegal immigrant accepts this exploitation because it is preferable to near-starvation in rural central Mexico and because the person wants a better life for his family back home. He knows, too, that much is forgiven in the United States to those who manage to rise out of poverty. Though most of the immigrants return to Mexico by choice, they are mindful of others (like the Los Angeles restaurant owner who had been deported 37 times) who were allowed to stay after becoming financially successful in this country.

More often than not, the U.S. citizen of Mexican ancestry feels a kinships to this immigrant, at least in the geography of his mind. Many of the oldest citizens themselves were immigrants. Some of the newest citizens still have relatives in Mexico. At the same time, American citizens with brown skin resent the police suspicion of them that illegal immigration brings and the necessity to constantly demonstrate at random checkpoints that they actually are legal immigrants or citizens.

Between the extremes of the wages illegals will accept and the wealth of a few Mexican-Americans such as New Mexico landowners who trace their heritage back to the conquistadors, Mexican-Americans are highly visible in agriculture, where their pay and working conditions have been vastly improved during the past decade by the efforts of the United Farm Workers. They also are conspicuous in Texas plywood mills, southern California factories and in garment and electronics plants that are strewn along the border from San Diego to Brownsville, Tex. A growing Mexican-American middle class is making inroads in small business in teaching and in government jobs.

The rise of this middle class and the overall Mexican-American population increase have been sharply reflected in the marketplace. The magazine Sales Marketing Management estimates that the Hispanic market has grown 23 percent since 1970, while the national market grew 4 percent. Now, there are national television ads in Spanish for Chrysler cars and Kentucky Fried Chicken. In MexAmerican, Spanish or bilingual billboards and store displays are used to sell beer, radios and razor blades.

Poor or insufficient education seems to be the major barrier to continued growth of the middle class and to full economic opportunity for Mexican-Americans. The statistics tell the story in Diboll, Tex., where 16 percent of the eighth-graders and only 9 percent of the ninth-graders are Mexican-Americans. "We need to develop an academic tradition like the Jews>" said Garcia. Instead, there often is a tradition of teenagers dropping out of school to help their large and closeknit families.

George pla remembers coming to East los Angeles at age 6, the son of an illegal immigrant laborer who became a contractor. Pla was placed in classes for the retarded because he couldn't speak English. As he learned the language, he moved out of the retarded classes. When he was 18 his parents debated whether he should work to help the family or continue his education. Pla wound up going to the University of Southern California and, at 28, becoming assistant director of business and economic development for the state of California. He also heads the Mexican-American Alumni Association at USC, a group of 250 that is raising $100,000 a year to fund 400 scholarships.

The Anglo-American community appears ready to accept the achievements of a well-off Garcia or a Pla. Many Anglo-Americans, however, are freightened by the idea of unceasing immigration from south of the border. Throughout the Southwest, the issue of illegal immigration arouses deep emotions among Anglo-Americans and reinforces stereotypes that portrays persons of Mexican ancestry as pickers of fruit and drawers of water.

"State Threatened by Alien Horde," read the banner headline in the Los Angeles Herald-Examiner last Aug. 8. The story, carried on The New York Times service and appearing the same day in several western newspapers, said that "a horde of destitute migrants from the Mexican interior" was massing at the border determined to reach the United States before a limited amnesty plan for illegal immigrants proposed by President Carter was passed by Congress.

Neither the "hordes" nor the amnesty plan has emerged in the seven months since this story, but the fear is a recurring one that until recently also reflected official U.S. policy.

"It's a national dilemma that threatens to worsen rapidly," said Leonard Chapman, director of the federal Immigration and Naturalization Service during the Ford administration. 'We're facing a vast army that's carrying out a silent invasion of the United States."

Chapman in 1976 estimated that the "invaders" had succeeded in establishing a beachhead of 12 million illegal immigrants in the United States. This estimate topped the earlier high figure of 8 million in a well-publicized report by Lesko Associates of Washington, D.C.

In the past two years, a variety of less-publicized studies have been steadily revising these estimates downward. Leonel CastillO, the present INS director, uses an estimate of 3 million to 6 million, a range so broad it is nearly meaningless. A recent report by the Population Research Center at the University of Texas estimates that there are 4 million illegal immigrants in the United States.

Nobody really knows the extend of illegal immigration from Mexico. Says Barry Fadem, director of the California Office of the Southwest Border Regional Commission: "If you talk about hordes, you use the 12 million figure; if you talk about economic contribution, you use the 4 million."

But if little is known about the actual numbers of the Mexican migration, such has been learned about the character, motiviation and economic impact of the migrants.

Studies by U.S. and Mexican sociologists show that most of the migrants come from poor, rural areas in teh Mexican interior and that, in the tradition of earlier immigrants to the United States, they are apt to be the "risk-takers" of their communities. These studies show that as many as 70 percent of the migrants return home after working a few months in the United States.

Other studies, including a recent one in Orange County, Calif., dispute the notion that illegal immigrants are a burden on U.S. taxpayers. Most of the migrants, this report found, pay considerably more in state and local taxes than they take out in social services.

One of the most intensive studies, by Wayne Cornelius of Massachusetts Institute of Technology, also contradicts the prevailing view that U.S. citizens are displaced from their jobs by the migrants. Once this may have been true; but improvements in welfare benefits and unemployments insurance have made the low-paying jobs held by the illegal immigrants distasteful to native Americans, whether white, black or Mexican-American.

"Most of the jobs in question are the least desirable in the U.S. labor market," found Cornelius. "They involve dirty, physically punishing tasks, low wages, long hours, generally poor working conditions, low job security and little chance for advancement."

Illegal immigrantion can perhaps best be regarded as a covert economic bargain that benefits everyone involved. It is beneficial to the immigrants, who even at $2 an hour earn three times what they might make in their homeland. It is beneficial for the big growers, the hotel owners and the factory managers, who have a huge, cheap source readily available labor that is in no position to complain about pay or working conditions. And it is undoubtedly beneficial to Mexico, providing a safety valve for that country's rural poor and discontented.

Within the Mexican-Aermican community itself, the continuing illegal immigrantion is a source of pride and concern. Most Mexican-Americans express ethnic satisfaction at the achievements of the migrants and revulsion at the scare stories that depict them as an alien people. Some Mexican-Americans believe that the presence of too many illegal immigratns in this country diminishes the chances of their own children for an education.

Others see the continued migration as a source of pressure to maintain bilingual education programs and other services helpful to Mexican-Americans and Mexicans. And for many the reality and memory of Mexico is near enough that they are inclined to cheer, publicly or secretly, for the success of the more recently arrived. "I'm king of proud that my parents were illegal immigrants," said Pla. "Maybe it's because I made it."

In the years to come, hundreds of thousands of persons like Rich Garcia and George Pla seem certain to "make it" in the middle-class world.Other thousands will do what Pla's parents did two decades ago and come north in search of a better life. For the one overwhelming reality on which everyone seems to agree is that the migration will continue as long as the United States is a rich country and Mexico a relatively poor one.

"The obvious thing to do if you listened to the people burning crosses would be to put up a wall down there," says historian Ramon Eduardo Ruiz. "That isn't going to happen. Aside from what it would do in this country, think of what it would do to the stability of Mexico, the peace and order of Mexico, to all the American investments in Mexico. You'd have an explosion there. No one in his right mind is going to be foreclosing the border."

Next: Oppression CAPTION: Picture 1, Migrant workers such as these in rosebeds near Wasco, Calif., have become highly visible in agriculture, By James M. Thresher - The Washington Post; Pictures 2 through 4, Mexican laborers wait on a street corner in San Antonio for anyone in need of inexpensive day workers. As a truck pulls up, they negotiate with the driver to hire them, usually for $2 an hour or less. Some are luck and get the ride., Photos by James M. Thresher - The Washington Post; Picture 5, Four workers try to get in a car whose driver needed only a few day laborers.; Picture 6, Rich Garcia heeded his father's advice, now is an aide to San Diego's Mayor,; Picture 7, Construction worker Jose Soto rides home after working in San Antonio, AP photos; Picture 8, Many Hispanics have found work in the garment industry, for example, making swimsuits in an East Los Angeles shop.