Few here were surprised when the United States Census Bureau announced that Los Angeles had officially overtaken Chicago as the nation's second city. Marketing studies had already shown Los Angeles to be most populous metropolis after New York City. And Los Angeles is so sprawling that the name usually refers to the whole basin, an agglomeration of nearly 8 million people - a mass unrivaled except by New York City.
Census estimates, released last weekend, showed that between 1980 and 1982, Los Angeles grew 1.8 percent to 3,022,247. Chicago, which has been the nation's second city since 1890, shrunk 0.2 percent to 2,997,155.
Second-city status, of course, is mainly symbolic.
Chicago, Carl Sandburg's ''City of the Big Shoulders,'' has been called the most American of American cities. In recent years, Los Angeles has been hung with that most-American label. But the Big Orange represents a different America than the Windy City.
Los Angeles is the flagship of the Sun Belt cities, especially those in the West, with their growing populations, high-technology industries, independence from political parties, rising Hispanic influx, post-World War II architecture, and the sprawl that comes from maturing in the age of the automobile.
The rise of cities with this kind of profile is reflected in the other Census Bureau estimates. Houston has shown the fastest growth of any major US city by swelling 8.2 percent in two years to 1,725,617. It surpassed Philadelphia to become the nation's fourth largest city.
Dallas, San Diego, San Antonio, and Phoenix, Ariz., each grew more than 4 percent between 1980 and 1982, and all are now among the 10 largest cities in the United States.
The Americans who move to these Sun Belt cities are mostly young, according to demographer Kevin McCarthy of Rand Corporation. They are joined by an older group of recently retired people, many of whom will return later to their hometowns to be near families, he says.
But growth in the very largest cities like Los Angeles is a little misleading , Dr. McCarthy adds. Los Angeles itself is only growing because of foreign immigration, he explains. During the 1970s, the city actually lost roughly 700, 000 native-born Americans.
Not surprisingly, Chicago and Los Angeles show different ethnic profiles. Chicago is half white and 40 percent black - more than twice the 17 percent share of black people living in Los Angeles. Los Angeles, in turn, is 60 percent white and has roughly twice Chicago's share of residents of Spanish origin (27 percent to 14).
Chicago has a greater share of first-generation Americans among its white ethnic communities and has five times as many residents who are Polish on both sides of the family. Los Angeles, though, has three times as many Asians and Pacific Islanders.
Is the proverbial Tinseltown a wealthier place? Incomes in the two cities are probably similar, McCarthy says. ''People tend to think of Los Angeles as a white-collar city. It really isn't. It's a blue-collar city.''
In fact, he adds, although Los Angeles is growing and Chicago is not, ''in general, you might expect a place like Chicago to have higher incomes because of the unionization factor.''