By Dean E. Murphy / The New York Times
 

WHITTIER, Calif., Feb. 13 The maternity ward at Presbyterian Intercommunity Hospital is one of the hottest bookings in town.
 

"Sometimes we have to float the postpartum moms to the third floor and the second floor wherever we can find a room," said Dr. Jaime Lopez, an obstetrician and gynecologist, sipping a cup of coffee after delivering his third baby in 24 hours.
 

On average, nearly a dozen newborns are delivered each day at the hospital's Ruth B. Shannon Maternity Ward, which opened eight years ago with 32 beds and almost every convenience imaginable.
 

But what impresses demographers about maternity wards like this one are the names scribbled on the patient board: Garcia, Sanchez, Martinez, Ortiz, Morales, Ramos and Vargas.
 

About 60 percent of babies at Presbyterian Intercommunity are born to Hispanic mothers. While hospitals serving East Los Angeles have long admitted large numbers of Hispanic patients, it is in suburbs like Whittier founded by Quakers, once home to Richard M. Nixon and for most of its 116 years decidedly middle class and white that the face of California is changing radically.
 

A survey released last week of birth certificates statewide showed that for the first time since the late 1850's, just a decade after California was seized from Mexico in the Mexican-American War, a majority of newborns are Hispanic.
 

More than two-thirds of the Hispanic babies are being born here in Los Angeles County and surrounding Southern California.
 

David E. Hayes-Bautista, director of the Center for the Study of Latino Health and Culture at the University of California at Los Angeles, which conducted the survey, said the 50 percent threshold was passed on July 4, 2001. As recently as 1975, Hispanic births accounted for just a quarter of the statewide total, Dr. Hayes-Bautista said.
 

The milestone, though long anticipated, carries great significance in symbolic and real terms, as Hispanics increasingly define what it means to be Californian, and American-born Hispanics assert numerical and cultural dominance over their immigrant counterparts.
 

"I broke the family tradition and didn't work for the railroad," said Dr. Lopez, a third-generation Mexican-American who moved to Whittier from East Los Angeles, where his mother lives in the neighborhood where he grew up. "My generation spoke English at school and we were able to leave the community. But for all Mexicans, the culture of la familia remains strong."
 

Dr. Hayes-Bautista and other researchers suggest that California is becoming the country's Hispanic heartland, where the American and Hispanic cultures are melding into something singularly Californian much as the Midwest was defined in previous centuries by immigration from northern and central Europe.
 

This new Californian identity is still evolving, but researchers and demographers say it may encompass everything from bigger families to longer work weeks to greater trust in government institutions. Research at the U.C.L.A. medical school even suggests possible shifts in health care needs, since Hispanic Californians tend to live longer than non-Hispanics and they are less likely to die from common killers like heart disease and cancer.
 

"What I see more than anything is a new American regional identity as distinctive in the future as Texas regional identity is right now, or Southern regional identity was," Dr. Hayes-Bautista said. "When people say today, `Oh, Latinos do that,' they will say in the future, `Oh, people from California do that.' "
 

That California has a large and growing Hispanic population is well known. The 2000 census showed that about one-third of the state's 34 million residents identified themselves as Hispanic, by far the largest Hispanic population in the country. During the 1990's, for the first time since early statehood, non-Hispanic whites in California became a minority.
 

But the Hispanic birth statistics point to a related trend that is less understood and, researchers say, potentially more meaningful.
 

For many years, immigration was the driving force behind the Hispanic population growth. Now, it is being driven largely by births. A report by the Pew Hispanic Center in Washington, drawing on Census Bureau projections, predicts that Hispanics born in the United States will account for about 13 percent of the country's population by 2025. Those born in other countries will account for only 5 percent.
 

As past immigration waves have shown, the differences between immigrants and their American-born families can be enormous. American-born Hispanics in California are already recasting what it means to be Hispanic in everything, including language proficiency and home ownership.
 

American-born Hispanics tend to be wealthier, better educated and socially more liberal than their immigrant parents or grandparents, research and public opinion surveys have shown. They are more likely to live in a house they own and without members of their extended family.
 

"I have third-generation Latino kids in my classes," said Harry P. Pachon, president of the Tomás Rivera Policy Institute at the Claremont Colleges in Claremont, Calif. "I ask them do they speak Spanish? They say no. Do they eat Mexican food? They go to McDonald's. Do they like rancheras music? They listen to Power 106," a Los Angeles pop music station.
 

But the assimilation process is constantly changing and it is difficult to know when it might suddenly shift into reverse.
 

Dr. Pachon said a survey by his institute showed that Roman Catholic Church attendance dropped among Hispanic immigrants' children, but spiked upward among in the grandchildren, who reported relying "a great deal on religion for day-to-day living" even more than their grandparents did.
 

At the same time, attitudes about church activism became distinctly Americanized with succeeding generations. The survey found that nearly 63 percent of immigrants believed the church "should be more involved" in social, educational and political life, while only 49 percent of their grandchildren expressed the same view.
 

One of the biggest unknowns in predicting a future California is the high rate of marriages among American-born Hispanics and non-Hispanics. Dr. Pachon said that only 12 percent of Hispanic immigrants marry non-Hispanics, but by the third-generation, the number grows well beyond 50 percent.
 

Here in Whittier, Dr. Lopez, the obstetrician, sees the trend up close. One of his appointments this morning was with Elianna Rivera-Jacobs, a 25-year-old second-generation Hispanic who is married to an African-American.
 

"Times are changing," said Ms. Rivera-Jacobs, who is expecting a girl. "My child is going to be mixed, and I feel there is good opportunity for her out there."
 

In suburbs like Whittier, where Hispanics, many of them well-to-do, now constitute a majority of the population, the demographic revolution has rallied many established Hispanics to shape the future.
 

One volunteer group here, the Hispanic Outreach Taskforce, held its annual advisory board meeting this week, at which Hispanic businesspeople, judges, public officials and educators took an oath to serve the area's growing Hispanic population. The group holds health fairs, offers college scholarships and assists teen-aged mothers.
 

Martin Ortiz, who recently retired as the director of the Center of Mexican-American Affairs at Whittier College, said the community efforts had made a big difference. When he arrived in Whittier as a student in 1947, the only Hispanic in his class, Mr. Ortiz said, he was stopped by someone on campus who asked what he was looking for.
 

"I said, `I am looking for an education,' " said Mr. Ortiz, who is now 83. "He looked at me with bewildered eyes."

This year, 320 Hispanics are among the college's 1,206 undergraduates. "Now the problem is different," Mr. Ortiz said. "You speak to those students in Spanish and they wonder what you are talking about."