The wedding party stood on the old stone steps of Sacred Heart Church -- the bridesmaids in turquoise lace, the bride and bridegroom smiling for the cameras of their friends. Forty years ago, this stately church near 16th Street NW in Mount Pleasant was the fashionable parish for Washington's Irish Catholic community.

Now the parish is nearly half Hispanic, and on this particular Saturday, it marked the wedding of Anselmo Reyes, a busboy, and Mirian Gonzalez, a housekeeper -- young Salvadorans who met and fell in love here, who may well raise their family here.

The suburbs, too, are different now. In Arlington, a drive up Columbia Pike is a tour of a suburban boulevard gone ethnic. Along with the car dealerships and the fast-food chains are a Thai supermarket, a Salvadoran restaurant, a Middle Eastern nightspot with belly dancing, and a jewelry shop where a Cambodian family sells tiny gold Buddhas and bolts of silk.

Summit Hills Apartments on 16th Street in Silver Spring is no longer home to the Jewish families who moved there in the 1960s, when it was the latest in high-rise living. Now the former synagogue at the complex is a day care center filled with nearly 60 children -- Salvadorans, Ethiopians, Guatemalans, Nigerians, Liberians, American blacks.

This is the Washington area in 1987: repeopled, redefined, undergoing a stunning cultural and economic transformation because of the arrival in the past decade of a record number of immigrants. Since 1970, the proportion of the population that is foreign born has tripled. Since 1980, it has doubled.

It is a dramatic change in character for Washington. For the better part of two centuries, the region has been largely black and white; the city itself, an inward little government town built on a federal economy. It held little lure for immigrants, and the standard complaint has always been its lack of diversity, of "ethnic neighborhoods."

Now, with the abundance of jobs of every sort, it is one of the nation's prime magnets for immigrants. Already the region is home to the nation's third-largest concentration of Central American immigrants, the fourth-largest group of Koreans and the largest group of Ethiopians outside of Africa.

Already the area supports a Spanish radio station, two Vietnamese newspapers, five Buddhist temples and an estimated 85 Ethiopian-owned businesses. A new infrastructure of ethnically based mutual assistance organizations, such as the Indochinese Benevolent Association, has taken root. There are 21,000 Hispanic and Asian adults learning English in special classes, and at least 43,000 Hispanic and Asian students enrolled in local schools. At 12 public schools in the region, at least half of the students are foreign born.

The change has been faster and larger than anyone predicted. In 1970, about 4.5 percent of the area's population was foreign born. By 1980, the proportion was up to 8 percent, or 250,000.

Seven years later, in part because of the arrival of tens of thousands of refugees from war-plagued El Salvador, experts now estimate that there may be as many as 450,000 foreign born in the area -- Hispanics, Asians, West Indians, Africans and Middle Easterners, amounting to roughly 12.5 percent of the metropolitan area's 3.6 million people.

Also striking are the prospects for the next 30 years. The Washington area could become a region where no one ethnic group holds a majority, demographers speculate. By 2020, Hispanics and Asians could account for nearly 1 million area residents.

War, revolution and poverty, the same age-old forces that have produced record migration to the United States generally, have prompted the new flow of people. The new immigrants have come here from at least 61 countries, but the greatest movement has been from Laos, Cambodia and Vietnam after the end of the American presence in Southeast Asia in the mid-1970s; from Ethiopia after Marxists took power from Emperor Haile Selassie in 1974; and from El Salvador, after the outbreak of bloody civil strife that intensified in the late 1970s.

The latest acceleration is due mainly to a historic and largely illegal influx from El Salvador. The size of that group can only be guessed, but most observers think the Salvadorans now account for about half of the region's 200,000 to 250,000 Hispanics.

The factors drawing them to Washington have been the presence of friends and relatives who arrived here before them, the special attraction of a national capital, and above all, the region's reputation as a rapidly expanding job market.

The phenomenon is as much suburban as it is urban, with as many as two-thirds of the newcomers living beyond the District line, where there are jobs and affordable housing.

While Hispanics still settle in the Adams-Morgan and Mount Pleasant areas and Asians still congregate in Arlington, there are also Vietnamese in Beltsville, Salvadorans in Manassas, Laotians in Laurel, Guatemalans in Gaithersburg.

They live in high-rise buildings ringing the Capital Beltway and in suburban split-levels bought with the earnings of two jobs and 60-hour work weeks, as well as in crowded city tenements.

Although the impact of their presence has yet to be assessed definitively, some trends are becoming clear:Small businesses, run by immigrants, have sprouted everywhere, thousands of them. Korean American business associations estimate that 2,000 convenience stores, dry cleaning shops and groceries are owned by immigrants from Korea; Hispanic organizations place the number of Hispanic-owned enterprises at about 2,300; Ethiopians are said to own 85 businesses.

This intense new small-business activity has also created new points of tension between these latest arrivals and blacks in the city -- a tension that has flared from time to time in controversy. The labor market is being redefined. The woman popping corn at the movie theater is Pakistani. The parking lot attendant used to be a customs official in Vietnam. The people fixing submarine sandwiches containing meats their religion says they may not eat are Lebanese. The owner-supervisor of the office cleaning crew is the former Ethiopian ambassador to France. They are Washington's new working class -- starting at the bottom in the area's booming service and construction industries. A new population "at risk" is being created, particularly in the city. Its nucleus is formed from tens of thousands of illegal immigrants, largely Salvadoran, who arrived after the cutoff date for amnesty under the new immigration law and are ineligible for refugee status because of government policy. They tend to be undereducated, underemployed and underserved by social services. Their fate is of deep concern to those who worry about the city's future. The schools have acquired a wholly new mission of educating children who speak little or no English, of helping them adjust to a strange new environment. Some schools have been transformed into acculturation centers for students, some of whom arrived traumatized by war and dislocation. School systems have taken on the task of educating parents on such mysteries as the American report card, the field trip, basic hygiene and nutrition. Finally, the area once derided by residents and visitors alike as homogenized and sterile has now indisputably a far more diverse, a far richer fabric. If the recent immigration is a story of a changing region, it is also a story of changed individuals, wrenched from their homes, their families splintered, their familiar lives vanished. They are here because farm workers in their home country make $400 a year, because political unrest made life intolerable, because they had to leave home or be killed.Poverty, Unrest and Death Squads

Jose Hernandez, 19, said he is here because battles between guerrillas and the military took place just outside the family's door; Mario Gonzalez, 20, because "the death squads were looking for me"; Arsenia Blanco, 35, because she wants her three young children to have "a good life."

All three have settled in the Mount Pleasant area, where a three-block business district has taken on the appearance of a small Central American town. The sidewalks are filled with people in the evenings. Cars there are double-parked, small groups gather in doorways, an impromptu band plays in front of a Latino market. At Arcos del Espino, a Salvadoran diner, an elderly man in a straw hat and white shirt moves from table to table, telling a story with waving arms; upstairs, a young man sits in an open window, pool cue in hand. Signs outside plead for the return of a gatico perdido -- lost kitten.

In the small "Pigeon Park," a young Guatemalan in work clothes sits on a bench, his little girl on his knee, his neighbors lounging around him. In the dusty field at nearby Lincoln Junior High School, dozens of teen-age boys, most of them Salvadoran, play soccer in the deep blue twilight. Younger brothers watch from the sidelines.

There is no single "trend" that captures the experiences of the new immigrants. So much depends on circumstance, on timing.

Consider Jose Reyes, who came illegally from El Salvador 13 years ago but is now a naturalized American citizen. He owns three restaurants in the city.

"I'm very content here," he said. "I'm very happy with this country."

Other Salvadorans, who happened to arrive illegally in the past few years, now seem ineligible for everything: for amnesty under the new immigration law, for refugee status, for jobs, for services, for promising futures.

America, some of these new arrivals have discovered, can be an unfriendly place. "Very often, I hear them characterize Americans as very cold," said Eduardo Lopez, a Salvadoran who is now an official in the District's Office of Latino Affairs. "In Latin America, the family, the group, is everything. You're always going out with your cousins, your uncles. They come here and they see that neighbors don't talk to each other. It's hard to make friends. The circles seem so tight. The language is strange.

"They are, I guess, intimidated, in awe of everything."

Many of the immigrants speak of learning new lessons about life, of a new "humility," as Haile Tasew, an Ethiopian, put it.

Tasew, the former Ethiopian ambassador to France, is a tall, thin man with a deep voice, speaking in measured English. He defected from his Marxist-ruled country six years ago. Since then, the honors graduate of the University of Wisconsin has worked as a paralegal, a substitute teacher and an English instructor to new immigrants in Alexandria and Arlington.

"We have to approach everything now from a position of humility, simplicity and courage," he said. "Humility, because we can't expect to have the jobs we had before. Simplicity, because the life we enjoyed is gone. Courage, because leaving a people you have loved -- leaving a country you have loved and respected and still love -- does require the courage of conviction."

These days, Tasew is concentrating on his new venture, an office-cleaning firm called Star Maintenance. His six part-time employes are Central American immigrants.

Ui Soong Kang, a quick man who is polite to even the rudest customers, smiles and nods and shrugs when customers remark on the curiosity of his business: bagels.

"Sometimes people say, 'You are Oriental people. Why do you own a bagel shop?' " said Kang, 40. "I didn't even know what a bagel was until I bought this business. But it is a good business."

Five years ago, he was a bank clerk in Seoul. His wife Dongju was a college teacher. Living with three close relatives, Kang first worked two jobs -- full time as a kitchen helper in a Georgetown restaurant, part time as a clerk in a McLean convenience store.

Two years ago, he sank his savings into a failing bagel shop and turned it around with 90-hour work weeks. Only a month ago, the father of two young sons took the next step, the purchase of an old four-bedroom house on a small lot in Rockville.

Some, such as Golden Hiep, the owner of Phnom Penh Jewelry, are now American citizens, but they can't help but look back.

At his jewelry store, he pressed a button activating the electronic door and allowing a visitor inside. The shop, small and newly renovated, has deep-red carpet and sleek glass display cases. On the walls are a business blessing -- gold Chinese characters on a red plush background -- and a large tapestry of a Buddhist temple in Cambodia that was built in the 7th century.

In a soft voice, Hiep, 51, described his first five years as a hot dog vendor behind the Capitol. He calmly ignored the comments of the oldest of his six children, a wry 22-year-old who answered a question about her social life with a gesture toward her parents. "Fun? What fun? With these two?" He fought back tears as he talked about his unsuccessful two-year effort to bring his ailing 80-year-old father to America.

Hiep is the first to say that this country has been good to him, that he has worked hard and prospered, and that he was honored to become an American citizen two years ago. But does he feel that this is his home?

He smiled. The smile was faintly apologetic. "This is my second home."

Reliable numbers about the new immigrants in the Washington area do not exist. The numbers used in this series come from the estimates of community leaders, immigration officials and several demographers consulted by The Washington Post. They are based on a recent U.S. Census report that says the region's population grew from 3.2 million in 1980 to 3.6 million last year.

The census report, however, contains no information on changes in ethnic composition. Leon Bouvier, former staff demographer for the Select Commission on Immigration and Refugee Policy, suggested these breakdowns for a 1986 population of 3.6 million: 2.2 million non-Hispanic whites, virtually unchanged from 1980; a million blacks, compared with 870,000 in the last census; 250,000 Hispanics, a dramatic increase from the admittedly low 1980 count of 90,000; and 150,000 Asians and others.

This census category -- "Asians and others" -- is composed largely of Koreans, Vietnamese, Chinese, Filipinos and East Indians. It also includes growing communities from the Middle East and Africa, notably a large Iranian community, and the largest group of Ethiopians outside Africa.

While stressing that the future is uncertain, Bouvier provided one scenario based on recent trends. When the metropolitan D.C. area reaches 5 million, a possibility by 2020, whites would make up 50 percent of the population; blacks would hold at 30 percent. Hispanics, the fastest-growing group, would account for 12 percent; Asians and others, 8 percent.

"It could well work that way," said local demographer George Grier, an authority on population trends in the Washington area. Everything Was Black and White

If Washington is now a magnet for immigrants, its previous ethnic history was distinctively black and white.

The capital was created in 1790 from portions of Maryland and Virginia, two states with high concentrations of blacks. The black density, first in the city and later in the region, has always averaged about 25 percent -- consistently near the top among urban areas.

Earlier immigrants usually bypassed Washington because its specialized economy offered them little opportunity, though the city did receive a large group of Irish immigrants who came in the 1850s to build the Chesapeake and Ohio Canal; they were followed in the late 1800s by Germans, Italians and some Eastern Europeans.

Washington's ethnic mix remained stable even when most American cities were transformed by the great wave of immigration that brought 23 million Europeans to the United States from 1880 to 1920. Washington, an outsider in the age of industrialization, had a foreign-born population of only 8 percent in 1890; by contrast, Milwaukee was 38 percent foreign born.

In the 1920s, the record era of national immigration ended with a series of laws that sharply checked further immigration for the next 40 years.

Then came the Immigration Act of 1965, which eliminated the ethnic bias of the past by giving equal opportunity to all countries. What's more, it made family reunification its overriding goal and placed no ceiling on the immigration of close family members of citizens.

The outcome, triggered by pressures in the Third World, was the nation's second great wave of immigrants.

Since 1979, annual totals of new immigrants have approached record highs nationally -- possibly a million a year including illegal aliens, whose flow the new immigration law is designed to stem. Hispanics and Asians make up more than four-fifths of today's newcomers both nationwide and locally.

Once again, the nation is being recast.

"Heavy immigration is the basic cause," said Carl Haub, director of demographic and policy analysis for the Population Reference Bureau, a nonprofit agency that reports on population trends. "But high Hispanic fertility and low white fertility are intensifying the ethnic shifts both locally and nationwide. The Hispanics are growing five times as fast as the rest of the U.S. population."

Washington's place in the immigration forefront can be traced to its emergence from World War II as a world capital. The region has since shown sharp growth, expanding first from a federal city of 1 million in 1940 to a metropolis of 3 million in 1970.

Thousands of new service jobs offer ready employment for immigrants often lacking education or English skills. In addition, Washington holds a special attraction for Asians and Hispanics whose cultures view the capital as a country's ultimate city.

Whether many future immigrants will start new lives in Washington depends on several factors, notably the local economy, which experts expect to continue expanding, and U.S. immigration policy.

Immigration nationally is expected to remain high, with legal immigration in the United States expected to reach 800,000 by 1990. The question of illegal immigration, which accounts for perhaps 300,000 people a year, is much more difficult. The Immigration and Reform Act of 1986, while granting amnesty to illegals who have lived in the United States for five years, was primarily aimed at discouraging other illegals. The law could have a major impact as enforcement picks up.

Despite such uncertainties, the pool of prospective immigrants will likely remain as pressing as the latest headlines: a new famine in Ethiopia; doubling in 20 years of the population in the Carribbean basin; continued turmoil in El Salvador and Central America.

"They're not going to go away," said Edgar Mantilla of the Montgomery County Human Relations Commission. "And they're going to keep coming."

Airport Vignette

It was a long, fidgety evening in the waiting area outside customs at Dulles International Airport. Jihad Achour, a Lebanese sandwich-maker, was laughing and cracking jokes about American culture: "Just call me Joe," he said to a friend.

Achour, 29, was about to see his father for the first time in six years. His brother and sister and four nephews have already settled in Washington; his father's arrival completes the family. Achour coolly downplayed his emotions as he watched the other passengers greet their relatives.

"Nervous? No," he said. "But I am happy."

And then, finally, his father appeared: a 68-year-old barber from Beirut wearing a pale blue leisure suit. He embraced his son for a long time. No one spoke.

A few minutes later, they headed for the parking lot, arm in arm, the father patting the son's back as they walked.

Next: The Schools: A Mission Redefined