OS ANGELES, June 9 — Long ago, in the Southern California of the Beach Boys and at least a few remaining orange groves, the San Fernando Valley was a grassy suburban enclave known for its overwhelmingly white population and resistance to racial change, particularly school busing.
Those were the days when white residents began the current struggle to wall themselves off politically from the minority-dominated inner city by seceding from Los Angeles.
That era of white flight is long over, but in the San Fernando Valley, now heavily Latino, the drive for secession is stronger than ever. The difference now is that much of the energy in this struggle is being spent not against Latinos, but among them.
Oscar Mendoza, 28, who grew up in the Valley and runs a construction company there, chuckled when he was reminded how the secession movement began. Mr. Mendoza enthusiastically supports it and hopes to push it to success this November.
As he strolled through his Sylmar neighborhood, where most of the signs are in Spanish, he explained that in today's Valley, secession is focused on resisting the distant and unresponsive power of the same City Hall that once fought to open the Valley for families like his. He said he even planned to run for the council of the new city.
"Whatever happened back in those years has nothing to do with the situation now," Mr. Mendoza said, noting that the Valley, like Los Angeles, now has a plurality of Latinos, about 45 percent. "The numbers, everything has changed. This will benefit everyone, including Latinos. In fact, it mostly helps Latinos."
The battle over Valley secession would transform the country's second largest city, slicing off roughly a third of its residents and some of its most solidly middle-class neighborhoods. It would energize other secession movements (Hollywood is also trying to separate itself) and could divide the city further into an array of competing municipalities.
Whatever the outcome, secession is also proving to be a test for Latinos, who are bitterly split by the issue as they have rarely been before. Some experts and community leaders have described the secession issue as a sign that socioeconomic differences now exert more influence over how Latinos vote than mere ethnic identity.
"This is not quite an ethnic issue any longer," said Alex Padilla, the president of the Los Angeles City Council and a staunch opponent of secession for the Valley, which includes his district.
"It's a bread and butter issue," Mr. Padilla said. "This is about the L.A. agenda, not a Latino agenda."
Latino voters in Los Angeles have come together on other issues — as in the campaign several years ago over a state proposition that would have denied many services to illegal immigrants, and last year's mayoral campaign, which almost brought to office the first Latino mayor in modern times. But this time, Latinos are not expected to vote as a bloc, not even close.
Although some polls have shown Latino voters leaning slightly toward secession, the battle lines are sharp, with the camp around Mr. Padilla bitterly resisted by the camp around another Latino leader, Richard Alarcón, a state senator from the Valley who has said he would consider running for mayor of the new city. Mr. Mendoza worked on Mr. Padilla's campaigns before joining the secessionist forces.
Harry P. Pachon, a professor at the Claremont Graduate University and president of the Tomás Rivera Policy Institute, said: "What this means is that, at least in Southern California, we have reached that critical mass where Latinos are no longer an isolated interest group protecting one way of seeing their interest."
Dr. Pachon added that many suburbs in the region that were once predominantly white are now heavily Latino, contributing to the swiftness of the political change, neighborhood by neighborhood.
"Even the 2000 Census is already out of date," he said.
Bearing the brunt of these changes is the mayor of Los Angeles, James K. Hahn. He won office only last year against Antonio Villaraigosa, the former speaker of the California Assembly, by cobbling together a makeshift coalition of more conservative whites from the Valley and blacks. Mr. Hahn won only 18 percent of the Latino vote.
But since then he has alienated many black supporters by fighting against a second term for the police chief, Bernard C. Parks, who is black. Realizing that he cannot stop Valley secession without a substantial part of the Latino vote, Mr. Hahn and his aides have shifted gears.
He has enlisted Mr. Villaraigosa's help, and he has sent his operatives to woo Valley Latinos. It is not proving easy, because Mr. Hahn did so little to win them over in the past.
"I quite frankly was terrified in meeting with certain groups," said Kam Kuwata, a political consultant who is helping lead the campaign against secession. "I thought it would be uncomfortable," Mr. Kuwata said.
"Latino voters could be the margin of victory."
The opponents of secession have sought to win over Latinos in part by pointing to the Valley's historic resistance to school busing, arguing that an independent Valley would still be hostile to them. But secessionist leaders have pointed to everything from potholed streets to slow police response times to argue that a smaller government would be more responsive.
"Secession is not an ethnic issue as much as it's more or less a tax revolt of sorts," Mr. Alarcón said. "This is coming from the grass roots, not some anti-busing folks who had other reasons for backing this. The Latino working people and the working poor feel this city's services are stressed, but that's not different from any other community."
Mr. Villaraigosa said that because most of the leaders of the secession movement were businessmen and the well-to-do, the new city could be less friendly to the working class — meaning Latinos — than Los Angeles is, undercutting rent control and social services for the working poor.
Xavier Flores, vice president of the San Fernando Valley chapter of the Mexican American Political Association, said the new city might have looser campaign contribution limits than Los Angeles. That, he said, would hand greater power to wealthy, largely white Valley residents.
He pointed out that the Valley's police force would not be bound by a rule in Los Angeles that prevents police officers from making immigration arrests. That could make the Valley hostile to new immigrants, legal and illegal, he said.
However it turns out, this battle is not between insiders and outsiders, said Richard Katz, a former City Council member and state senator who is helping lead the drive toward secession.
"What this is," he said, "is an opportunity to become part of a new power structure as opposed to those who have a vested interest in the status quo."