LOS ANGELES -- Antonio Villaraigosa, this city's telegenic Mexican-American mayor, is being buffeted by the politics of immigration.

Earlier in the year, Mr. Villaraigosa made an impassioned speech to 500,000 protesters who marched on City Hall. But when hundreds of thousands of mostly Hispanic people rallied on May 1, the mayor wasn't on the list of speakers. He was supposed to be flying to Dallas for meetings about bringing an NFL team to Los Angeles. Hours into the rally, a spokesman said he still wasn't sure about the mayor's plans.

So it came as a surprise when Mr. Villaraigosa, clutching a big American flag, took the stage in the early evening and addressed the marchers packing Wilshire Boulevard. "We all come here for the same reasons," Mr. Villaraigosa, the son of a Mexican immigrant, told the crowd. "We come to work. We come for a better life. We come to participate in the American dream." The mayor called for secure borders and "sensible and fair bipartisan immigration reform." Then, he rushed to the airport.

Los Angeles, a city where nearly half of all residents are foreign-born, has become a leading force in the nation's immigration debate, presenting the city's Democratic mayor with a problem. If Mr. Villaraigosa appears too sympathetic to the cause, he could be pigeonholed as an ethnically driven mayor by both blacks and white conservatives hostile to relaxing immigration laws. Yet appearing critical or even lukewarm about the matter runs the risk of alienating the mayor's biggest and most fervent base of support.

As the immigration debate gathered steam, Mr. Villaraigosa has tried to have it both ways. He has addressed rallies but also urged thousands of Hispanic kids to return to school after they walked out in late March, a move for which he was roundly booed. He also told protesters to carry American, not Mexican, flags during immigration rallies, and said he opposed the Spanish-language version of "The Star-Spangled Banner."

Mr. Villaraigosa is the first Latino to run Los Angeles in more than a century, the climax of a longstanding effort by Hispanic activists to gain a voice in city politics. During his frenetic campaign, however, Mr. Villaraigosa avoided championing the immigration cause and pitched himself as a mayor for all. His landslide victory included support from Westside liberals and inner-city blacks, and transcended racial, ethnic and class boundaries.

Any missteps on the immigration issue could jeopardize the mayor's long-term ambitions. "This movement is a threat to Antonio, who is trying to identify himself with Latinos but also wants to appeal to middle-class voters when he gets ready to run for governor," says Joel Kotkin, a senior fellow who specializes in urban issues at the New America Foundation, a think tank. Some people who know the mayor say he aspires to run for president.

In an interview, Mr. Villaraigosa demurs when asked about his role in the immigration debate. "I don't believe I am the leader or face of this movement," he says. "I just happen to be the mayor of a city that has a very large immigrant population."

Asked to spell out his position, he replies after a long pause: "I have the responsibility to say to this country that we should secure our borders, enforce our immigration laws and hold people accountable for breaking the law -- and also give people a path to citizenship who are paying their taxes, working hard and playing by the rules." His position, a mixture of tough and lenient, is in fact similar to that of President Bush. It might end up pleasing neither side.

In occasionally presenting a sterner posture, "Antonio the rebel and protester has gotten a little lost in Antonio the mayor," says Carol Sobel, a civil-rights lawyer who went to law school with Mr. Villaraigosa.

Since taking charge of the nation's second-largest city in July 2005, Mr. Villaraigosa has made it his business to be everywhere, courting its myriad interest groups in a way not seen since Tom Bradley, L.A.'s mayor from 1973 to 1993. During a day of citywide volunteer services organized by a Jewish congregation, Mr. Villaraigosa peppered his speeches with words such as "mitzvah," Hebrew for worthy deed, and "shul," Yiddish for synagogue. He recently posed for photographs donning a turban, alongside leaders of the city's Sikh community.

Last month, he brokered a deal between the Service Employees International Union and L.A.'s biggest commercial-property owner, paving the way for thousands of mostly black security guards to unionize. Both sides say the deal wouldn't have happened without the mayor's intervention.

"I don't think people have the perception that he is favoring any group," says Eli Broad, a billionaire businessman and philanthropist who contributed to the mayor's campaign.

The mayor's detractors say he's stretching himself thin with an ultra-ambitious agenda. Pet projects include taking control of the county's struggling school system and building a $2.7 billion subway to the sea, from downtown Los Angeles to Santa Monica. His daily schedule of appearances has also earned him a reputation as someone with a penchant for photo ops. On Good Friday he washed the feet of homeless people -- while wearing gloves -- in a downtrodden section of the city.

Mr. Villaraigosa was born Antonio Villar, the son of a Mexican immigrant and a second-generation Mexican-American. He grew up in Boyle Heights, an East Los Angeles Latino enclave also home to Jews and Japanese-Americans. Mr. Villaraigosa has repeatedly said he lived in a home where violence and alcoholism were rife. His father left when he was 5. Mr. Villaraigosa invokes his deceased mother, saying she infused him with the values that guide him.

When Mr. Villaraigosa was 16, a benign tumor in his spinal column briefly paralyzed him from the waist down, curtailing his ability to play sports. His grades plummeted at the Roman Catholic school he attended. The next year, he was expelled after getting into a fight.

Mr. Villaraigosa enrolled at Roosevelt High, a large public school in Boyle Heights, where he participated in student walkouts as part of the late 1960s Chicano movement, which fought for better access to education and employment for Mexican-Americans.

He dropped out for a semester, then returned in response to his mother's pleas. Mr. Villaraigosa eventually made it to junior college, thanks to a teacher's mentoring. He transferred to the University of California, Los Angeles where he honed his skills as an activist.

On graduating, he joined a circle of young Latinos who steadily ascended the city's labor movement and political hierarchy. "We would go out to organize immigrants," recalls Maria Elena Durazo, chief of the Los Angeles County Labor Federation, a labor-union umbrella group. Ms. Durazo is a key figure in the current immigration movement and a friend of the mayor.

After marrying a public school teacher, Corina Raigosa, in 1987, the mayor suggested they merge their last names, forming Villaraigosa (pronounced veeya-ray-GO-zha). They have two children; the mayor also has two daughters from previous relationships, and a grandchild.

Mr. Villaraigosa clinched a seat in the state Assembly in 1994. Four years later, he became speaker -- the first from Los Angeles in 24 years. When he decided to run for mayor in 2001, he had both Westside liberals and conservative voters in San Fernando Valley "in the palm of his hand," recalls David Lehrer, president of Community Advocates, a Los Angeles group that tries to promote better relations between the city's various racial groups.

But Mr. Villaraigosa lost a brutal runoff campaign against James Hahn, a veteran Democratic city politician. Mr. Hahn saturated airwaves with a TV ad featuring a grainy image of Mr. Villaraigosa interspersed with someone cutting cocaine with a razor blade and a letter Mr. Villaraigosa wrote in 1996 asking Bill Clinton to pardon a convicted drug dealer. The tag: "Los Angeles can't trust Antonio Villaraigosa."

In 2005, he battled Mr. Hahn again, despite a promise not to break the four-year term he had won on the city council. Latinos, who represent about 25 percent of the electorate, voted en masse for Mr. Villaraigosa. He also attracted more white and Asian voters than in 2001. Most importantly, he bested his rival among blacks, who had been loyal to the Hahn name for years.

That victory hasn't damped a big problem: the often-contentious relations between the city's Latinos and African-Americans. The stream of Latinos into black neighborhoods such as Watts has generated friction between two groups at the bottom of the economic ladder. Early this year, blacks and Latinos battled in Los Angeles jails, resulting in several deaths. There have also been some notable brawls in high schools.

As the mayor's attitude toward the immigrant cause comes under the spotlight, "there is a dicey road ahead in regards to the African-American constituency," says Sherry Bebitch Jeffe, a senior scholar at the University of Southern California's School of Policy Planning and Development. Many African Americans believe that illegal Hispanic immigrants rob them of blue-collar jobs and force down wages.

"Will he be a coalition builder ... or will he indeed become the Latino mayor?" asks Earl Ofari Hutchinson, an African-American political analyst who studies black-Latino relations. After Mr. Villaraigosa appeared to embrace the immigration movement, "questions came up again about his sympathies and loyalties," Mr. Hutchinson says.

On the morning of May 1, as thousands of Latinos began congregating downtown ahead of the marches, the mayor hosted a meeting with African-American leaders to discuss a range of issues, including job creation and school overhauls, especially in South L.A.

Among those in attendance was John Hunter, chief pastor of the First African Methodist Episcopal Church, which has 19,500 members. "The mayor is striving to represent every aspect of the community," says Rev. Hunter in an interview. Yet he also notes the immigration question could be a divisive one. "The African-American community is not completely together on the issue."

The following week, Mr. Villaraigosa convened a meeting with mainly white leaders of local construction trade unions to tell them "we have to get more African-Americans in the building trades and in apprenticeship programs." Construction jobs often go to Latin American immigrants, many of whom are in the U.S. illegally.

Despite efforts to placate critics, Mr. Villaraigosa has been pounded for every perceived misstep on the immigration issue -- and from all sides. At one rally, Mr. Villaraigosa argued that immigrant workers make the country run. They "clean your toilets," he told the crowd. Listeners to a conservative radio show mailed more than 1,000 toilet brushes to City Hall. "A lot of people look at Villaraigosa and they see an illegal alien," says KFI AM radio host John Kobylt, who opposes loosening immigration rules. "There's no end to how much we'll milk this."

After the massive March 25 rally, Mr. Villaraigosa appeared to take a tougher line with immigration protesters. When thousands of Hispanic students spilled into the streets that month to protest an immigration bill, the mayor urged them to return to school. The students booed him and refused to leave. Ahead of the May 1 rally, he called on parents to keep their children in school and for teenagers to stay in the classroom. He made it clear he opposed an economic boycott.

The mayor says he put himself in the shoes of parents who would want their kids in school. His aides add that Los Angeles school system can ill afford to lose state funding, which is tied to student attendance.

Mr. Villaraigosa says he isn't turning his back on the immigration cause. He also isn't letting it dominate his agenda. Last week, he was in Washington, D.C., lobbying for federal funds with the Los Angeles Chamber of Commerce. His trip happened to coincide with that of a range of groups calling for a "national lobbying day" for immigrants, as the Senate resumed discussions on a bill.

Mr. Villaraigosa didn't join them. He had to get back to L.A. to attend meetings about bidding for the Olympics.