LOS ANGELES — A generation ago, California voters approved a ballot initiative that was seen as the most anti-immigrant law in the nation. Immigrants who had come to the country illegally would be ineligible to receive prenatal care, and their children would be barred from public schools.

But the law, which was later declared unconstitutional by the federal courts, never achieved the goal of its backers: to turn back the tide of immigrants pouring into the state. Instead, since the law was approved in 1994, the political and social reality has changed drastically across the state. Now, more California residents than ever before say that immigrants are a benefit to the state, according to public opinion polls from the Public Policy Institute of California.

As Congress begins debating an overhaul of the immigration system, many in California sense that the country is just now beginning to go through the same evolution the state experienced over the last two decades. For a generation of Republicans, Gov. Pete Wilson’s barrages on the impact of immigration in the 1990s spoke to their uneasiness with the way the state was changing. Now many California Republicans point to that as the beginning of their downfall.

Today, party leaders from both sides, and from all over the state, are calling for a softer approach and a wholesale change in federal policies.

The state’s changing attitudes are driven, in large part, by demographics. In 1990, Latinos made up 30 percent of the state’s population; they will make up 40 percent — more than any other ethnic group — by the end of this year, and 48 percent by 2050, according to projections made by the state this month. This year, for the first time, Latinos were the largest ethnic group applying to the University of California system.

Towns that just a decade ago were largely white now have Latino majorities. Latinos make up an important power base not only in urban centers like Los Angeles, but also in places that were once hostile to outsiders. There are dozens of city councils with a majority of Latino members, a Mexican-American is the mayor of Los Angeles and another is the leader of the State Assembly. Nearly all of the 15 California Republicans in Congress represent districts where at least a quarter of the residents are Latino.

“The political calculus has changed dramatically,” said Manuel Pastor, a demographer and professor of American studies at the University of Southern California. “Immigrants are an accepted part of public life here. And California is America fast-forward. What happened to our demographics between 1980 and 2000 is almost exactly what will happen to the rest of the country over the next 30 years.”

Proposition 187, the 1994 ballot initiative, prompted thousands of immigrants to register to vote and ignited a generation of activists, including dozens who now hold public office or run immigrant rights organizations that lobby for change in federal laws.

“The fact that the Republican Party got identified with anti-immigration has made things very difficult for them,” said Mark Baldassare, the president of the Public Policy Institute of California, which closely monitors shifts in the state. “It is what is going on nationally now, but California started much earlier.”

He continued: “Today, you would really be hard pressed to even think of a group that would come out in favor of putting that on the ballot, let alone something that would gain traction or be endorsed by a major party. It seems voters have moved on to looking for solutions to something they recognize as an ongoing situation here.”

Most political observers say California is nowhere near the end of its political transformation. The share of white voters, who tend to be older, is expected to continue to decrease, while Latinos and Asians will make up more of the electorate.

“The question for the party is, Where are you going to get your new voters from?” Mr. Baldassare said of Republicans.

Even in Orange County, widely seen as the most reliably conservative bastion in the state, Republican officials are changing their tone. Scott Baugh, the chairman of the county party, said that if the language did not change, his party would be relegated to permanent minority status.

“To constantly refer to undocumented immigrants as illegals is very hostile and self-righteous,” Mr. Baugh said. “Let’s point out that while crossing the border without documents is illegal, a federal misdemeanor, being in this country as an immigrant isn’t a criminal act.”

Still, when Mr. Baugh made similar comments at the party’s county convention recently, he was not met with wild applause. Indeed, one could be forgiven for mistaking him for a liberal, a notion he dismisses with a scoff.

“We have to be looking at basic notions of justice and equity and fairness,” he said. “In many instances, these immigrants have been hired by American companies, so if you want to hang your hat on the rule of law, focus on that.”

Latinos had long been concentrated in the urban centers and agricultural areas of the state. But they have continued to move to the suburbs, particularly in the Inland Empire, the suburbs east of Los Angeles. There, Latinos have driven rapid growth over the last decade and make up more than two-thirds of many cities. Experts estimate that more than half of the immigrants who entered the country illegally have been in the United States for more than a decade.

Even as the demographics changed steadily for decades, the shift in voters came more slowly. But in the most recent election, exit polls showed that Latinos made up 25 percent of the vote in California, compared with 9 percent in 1994, Mr. Baldassare said.

In the Legislature, which has 120 seats, the Latino caucus now consists of 24 members, more than double what it was two decades ago.

Ricardo Lara, the chairman of the caucus, said he traced his own political involvement directly to the anti-immigration sentiment in the 1990s.

“I was a freshman in college, and suddenly there was a blatant attack on people like my parents,” said Mr. Lara, who grew up in East Los Angeles with other Mexican immigrants. “The so-called sleeping giant has always been awake, but they’ve been in our schools and colleges, and now we are really starting to run things.”

Perhaps nobody has seen this more clearly than María Elena Durazo, the executive secretary-treasurer of the Los Angeles County Federation of Labor, where Latino service workers are the primary source of growth for unions. Proposition 187 was “the perfect storm to anger and motivate a big number of Latinos, and once we had them coming out, we made sure they kept voting,” she said.

“Nobody had ever gone out to new citizens in the immigrant community, to poor working-class immigrants, but they turned out to be very reliable voters for us,” Ms. Durazo said. “People were always talking about low enthusiasm, but that is not what we were ever seeing. Now the rest of the country is starting to catch up.”

Ms. Durazo recalled the huge May Day protests in 2006, when thousands of immigrants lined the streets of Los Angeles. At the time, she said, organizers made a strategic decision to discourage the waving of Mexican flags and instead handed out American flags on street corners.

“We wanted to project what we feel — we’re working people who love this country and are staying here,” she said. “For a long time, we were living in no more than four or five states, but now, we are in the smallest towns of Georgia and Alabama. And once we’re there, it gets harder to ignore or hope that immigrants will just go away.”