The crowd roared. "I think you struck a nerve," McCain said.

"I tell you, I really get ticked," the woman continued. "You go into Lowe's and it says, Entrada."

In response, McCain said that he favors comprehensive immigration changes, but only after the borders are secured. The crowd cheered at the latter, but quieted when he went on to advocate a "temporary worker program" and the need to accommodate the estimated 12 million people already in the country illegally.

It was a delicate rhetorical dance, illustrating how the issue of immigration pulls McCain in two directions at once.

He was the architect of a failed Senate proposal that would have provided a path to citizenship for illegal immigrants, a policy that an angry conservative GOP base termed "amnesty." To placate them, McCain began stressing enforcement first.

Yet that new emphasis risks alienating Latino voters, who could be pivotal in several closely contested states this fall.

During the last three weeks, McCain has been tangling over immigration with Democratic candidate Barack Obama in separate appearances before major Latino civil rights groups. The struggle itself is a sign of the Hispanic vote's growing power.

In an appearance July 13 before the National Council of La Raza in San Diego, Obama said that McCain had "abandoned his courageous stand" on immigration in order to win the GOP nomination, and he promised he would be "a president who won't walk away from something important . . . just because it becomes politically unpopular." Obama said he wants to bring illegal immigrants "out of the shadows" and onto the path to citizenship.

Speaking to the same group a day later, McCain said he was still committed to revising immigration laws, noting he had risked "political suicide" by working with liberal Democrats on the legislation.

"Doing my duty to my country is its own reward, but I do ask for your trust that when I say I remain committed to fair, practical and comprehensive immigration reform, I mean it," he said.

Despite the bickering and some rhetorical differences, the two candidates are not all that far apart on the substance of such changes. Obama has voted for the border fence, for instance, and both men want to crack down on employers who hire undocumented immigrants.

Immigration has faded behind concerns over the economy and the Iraq war in national polls, but it remains a hot-button issue in some regions and among some voters, including Latinos.

Hispanics make up 15 percent of the U.S. population - the fastest-growing ethnic group in the nation, but one that lags in voting. Because the Latino population is younger than the national average and many immigrants are undocumented, Latinos will amount to just 9 percent of the eligible voters in November, according to a recent study by the Pew Hispanic Center.

Based on historic voting trends, the report projected that Latinos would account for about 6.5 of the electorate that turns out at the polls.

But Hispanics are strategically concentrated in a handful of states that are expected to be close: Colorado, Nevada, New Mexico and Florida.

"Make no mistake about it: The Latino community holds this election in its hands," Obama said at the La Raza conference. As he pointed out, 40,000 Latinos registered to vote in New Mexico did not go to the polls in the 2004 election, and Democrat John Kerry lost the state by fewer than 6,000 votes.

Obama's campaign hopes for a surge in Latino turnout, while McCain wants to capitalize on recent Republican inroads with Hispanic voters - and his own ties to the community as a senator from border-state Arizona - to hold down the Democrat's margin.

On July 11, McCain's campaign began running television ads aimed at Latinos there and in Colorado and Nevada, all states won by President Bush last time.

Obama was leading McCain among Hispanic voters nationwide 59 percent to 29 percent, according to a July 2 Gallup poll. The margin was larger in a more recent New York Times/CBS News poll.

"The political environment in the country is advantageous to Democrats right now, and Hispanic voters reflect that - they're very concerned about the economy and the war in Iraq," said Adam J. Segal, a marketing consultant who is director of the Hispanic Voter Project at Johns Hopkins University. Immigration is a "complicating factor for Republicans," Segal said.

As a group, Hispanics have been trending Democratic in modern elections, though Bush was able to cut into the party's usual margin in his 2000 and 2004 victories. Hispanic support for Democrats solidified in the 2006 congressional elections, when many GOP candidates took a hard-line stance against illegal immigration.

And so McCain makes sure to include in his standard spiel on the issue expressions of compassion for illegals, whom he calls "God's children" seeking a better life.

"There's a great thing about America, and that is that we welcome all cultures from all over the world," McCain said during the recent town meeting in Pipersville, Bucks County. "We are the great, great nation that brings people together from all different backgrounds and languages and cultures. And we love the Hispanic heritage. We love the Irish heritage."

The audience of about 1,200 at Worth & Co., a manufacturer of heating and cooling systems, stayed largely silent. In the next breath, McCain added that he thinks immigrants should learn English. The crowd applauded.