WASHINGTON – Immigration reform was once Sen. John McCain's signature issue – and a key ingredient in his maverick image. Democrats have largely avoided the subject, but there are signs they'll be using the issue this fall to challenge the Republican presidential nominee's maverick claim.

"Everybody's so scared to touch the subject, because in certain areas it's detrimental to somebody's political future," said Rep. Charlie Gonzalez, D-San Antonio. "It's an issue that legitimately should be addressed."

Hispanics are the fastest-growing segment of the electorate, and analysts predict turnout as high as 9 million, up from the 2004 record of 7.6 million. Their clout will be most felt in battlegrounds like Nevada, New Mexico, Colorado and Florida.

Last week, Democratic pollster Sergio Bendixen released data showing that in all those states but Florida, Sen. Barack Obama holds a strong lead among Hispanic voters, and immigration is a key reason.

Mr. Bendixen predicted that "when the debates start, there will be a lot of discussion." The first debate is less than two weeks away, on Sept. 26 at the University of Mississippi.

Much of the public supports comprehensive reform – beefed-up border security, combined with a new guest worker program and some form of legal status for most of the 12 million illegal immigrants already in this country. But opponents feel very strongly, and Mr. Obama would prefer not to stir them up.

Mr. McCain was once the Senate's top champion of comprehensive reform, despite fierce resistance within his own party. But the push for a deal fell apart last year, and to survive the GOP primaries, he adopted the hard-liners' view that border security and enforcement must come first. He even declared that he would now vote against his own bill.

Some immigrant advocates remain convinced that he's on their side, that his goals remain even if the tactics changed. But others say he is no longer a credible ally. They note that, with Mr. McCain's consent, the Republican Party platform adopted this month shuns comprehensive reform.

"The story of the Republican convention is John McCain's capitulation to the anti-immigrant forces in his party and how he's fundamentally changed his position on this signature issue," said Simon Rosenberg, president of NDN, a liberal think tank. "I think it belies the whole 'maverick' positioning."

Mr. Obama took Mr. McCain to task over the same point last week, noting pointedly in a speech to the Congressional Hispanic Caucus Institute that Mr. McCain had "abandoned his stance."

It was a rare moment in a campaign that has focused largely on the economy, energy policy and national security, though Mr. McCain, too, put a spotlight on immigration when he released an ad Friday aimed at Latinos. In the ad, aired on the Alma Awards, the National Council of La Raza's answer to the Emmys, he promised that "addressing the immigration problem will be a priority" if he wins.

He promised "practical and fair" solutions but made no mention of security, amnesty or the other sticky details.