Urban Areas Now Home to U.S. Majority : Population: Census report shows 50.2% live in large metropolitan regions. Los Angeles gains on New York City in population.

As small towns blur into suburbs and shopping centers sprout office buildings, as American cities spill outward and the nation distances itself even more from its agrarian roots, a majority of the populace for the first time can be found living within a large metropolis.

A 1990 census report released Wednesday found that 50.2% of Americans reside in huge semiurban swarms of 1 million people or more. In 1950, the first post-World War II census found that less than 30% of the population was living in urban areas.

The report said that nearly 125 million people out of a total population of 248.7 million live within 39 large metropolitan centers. Greater New York City, with more than 18 million people, is the largest of these areas. It is followed by the 14.5 million residents of Greater Los Angeles, a metropolis that by Census Bureau definition includes Long Beach, Riverside, San Bernardino, Anaheim, Santa Ana, Oxnard and Ventura.

Experts said the historic statistical shift is as much a signal of how Americans work as it is of where they live: big cities and their environs have expanded because of the growth of the economy’s service sector.

“America’s post-industrial economy has relied on the growth of management, research and development, marketing and distribution--areas that require the critical mass of educated people and services that you only find in large cities,” said Christopher Leinberger, a commercial real estate consultant who writes about the growth of cities.

Metropolitan expansion in the 1980s stemmed largely from suburban growth, fueled in Southern California by the availability of comparatively inexpensive housing and, in many other places, by the rapid expansion of businesses into outlying suburbs. One example of that is Tyson’s Corner, Va., once a spot on the map of Greater Washington, D.C., that now has more office space than Baltimore.

The sprawl has changed all kinds of boundaries, said Edward J. Blakely, chairman of the department of city and regional planning at UC Berkeley.

“The lines of demarcation between many towns are lost,” Blakely said, “and divisions between rich and poor and between the races are not the same. . . . You no longer have the rich living in suburbs and the poor concentrated in inner cities. . . . You now have ‘sluburbs’ “--a conflation of slum and suburb.

Urban sprawl is also leading to a new kind of segregation, Blakely said.

“As a society we are also becoming more fractured, relying less on a common subway, school system or sewer and water system,” he said.

Cultural changes also occur as small California towns--places such as Hemet and Victorville, Tracy and Folsom--lose their rural identity. Said Blakely: “Our traditional old non-metropolitan ideas, whether it’s growing up with farm animals or fishing in the old fishing hole, the way I did growing up in Colton, don’t stand a chance.”

In the past decade, the nation’s fastest growing large metropolitan areas--those with populations of 1 million people or more--included Orlando, 53%; Phoenix, 40%; Sacramento, 34%; San Diego, 34%; Dallas-Ft. Worth, 32%; Atlanta, 32% and Los Angeles, 26%.

While continuing to trail Greater New York in total population, the Los Angeles metropolitan region is growing much faster, gaining more than 3 million people compared to New York’s 547,000. The New York area includes Long Island and several cities in northern New Jersey and southern Connecticut.

If that trend continues, said Mark Pisano, director of the Southern California Assn. of Governments, the Los Angeles metropolitan area will surpass New York in population some time after the year 2010.

“The most important thing driving growth in the L.A. area,” Pisano said, “is an economy made up largely of high-tech industries, where the U.S. has a competitive advantage. We were the only region where the manufacturing base increased in the country, where the number of people employed in manufacturing actually grew.”

Elsewhere in California, fast-growing metropolitan areas identified by the census were Modesto, 39%; Stockton, 38.4%; and Fresno, 29.7%. The San Francisco Bay Area, encompassing Oakland, San Jose, Vallejo, Fairfield, Napa, Santa Rosa, Petaluma and Santa Cruz, grew by 16.5% to more than 6.2 million. It is the nation’s fourth-largest metropolitan region behind New York, Los Angeles and Chicago.

The Census Bureau defines metropolitan areas as “one or more counties including a large population nucleus and nearby communities that have a high degree of interaction.” In the 1990 census, metropolitan areas were divided into two groupings: those above 1 million population and those below.

The 1990 census counted four new metropolitan areas of 1 million or more people: Charlotte, N.C., Salt Lake City, Rochester, N.Y., and Orlando, Fla.

Florida experienced the most explosive growth of its large urban areas, according to the census. This stemmed from the expansion of its tourist industry and an ongoing tide of retirees. Besides Orlando, Naples, Ft. Myers, Ft. Pierce, Ocala, West Palm Beach, Melbourne and Daytona Beach all grew by more than 40%.

Las Vegas grew the fastest of smaller metropolises, defined as those with populations of less than 1 million. Las Vegas grew by 60%. Austin, Tex., grew by 46% and Las Cruces, N.M., by 41%.

The census metropolitan growth numbers tended to reflect the shift of the nation’s population west and south. In the east, at least four large metropolitan regions actually lost population: Pittsburgh, Buffalo, Cleveland and Detroit.

Experts said they believe the country will continue to urbanize during the coming decade, but that there will be a move away from the kind of formless sprawl that has characterized the trend.

“Already, many places are developing their own cultural institutions,” Blakely said of California’s suburban enclaves. Beyond that, he said, he expects to see many towns attempt to look more like old-fashioned cities.

“I would anticipate an increasing interest in making some of these places more urban in form, increasing their densities, bringing back old downtowns in places like Riverside and West Covina,” he said.