Barack Obama and John McCain will step up their battle for Latino support over the next two days, as they take turns appealing to a major Hispanic organization for the third time in three weeks.

The two presidential candidates have increasingly jockeyed for Latino voters, sensing that constituency could play a pivotal role in battleground states such as Colorado, New Mexico and Florida.

The next organization to hear their pitches is the Latino civil rights group National Council of La Raza. Obama speaks at the council's annual conference Sunday in San Diego, Calif. McCain follows on Monday.

Each candidate is using the national tension over immigration reform to bludgeon the other, and their upcoming appearances provide a platform for them to extend that battle.

McCain, who worked on comprehensive reform efforts in the run-up to his presidential bid, is pushing back hard against Obama, who described himself this week as a "champion" of such immigration legislation.

"The crux of the issue is, when the chips were down, when we were desperate to round up votes, Obama was killing comprehensive immigration by offering up a poison pill (of controversial amendments)," said Florida Sen. Mel Martinez in a McCain conference call. "Now he takes credit for the immigration effort. ... He was AWOL. ... Nothing could be further from the truth."

McCain aimed to court Latino voters Friday when he released a TV ad in Colorado, Nevada and New Mexico highlighting military service.

"When you go to Iraq or Afghanistan today, you're going to see a whole lot of people who are of Hispanic background," McCain says in the ad, noting that some of them are not even citizens but "love this country so much that they're willing to risk their lives in its service ... They must come into our country legally, but they have enriched our culture and our nation as every generation of immigrants before them."

McCain also recently returned from a trip to Colombia and Mexico, where he discussed immigration challenges facing both countries.

McCain, who took political risks in forging legislation with Democratic Sen. Ted Kennedy that would have provided a pathway to citizenship for millions of illegal immigrants, faces lingering skepticism from his own party as he appeals to Hispanic voters.

Conservatives will no doubt be watching closely when he addresses the National Council of La Raza, which has been criticized as having a permissive stance on illegal immigration.

McCain was notably silent earlier in the week when conservatives pounced on Obama for saying in Georgia that while immigrants should learn English, "you need to make sure your child can speak Spanish. ... We should have every child speaking more than one language."

Obama batted back the criticism Friday at a rally in Dayton, Ohio.

"The Republicans jumped on this. I said, absolutely immigrants need to learn English, but we also need to learn foreign languages," he said. "We should want our children with more knowledge. We should want our children to have more skills. There's nothing wrong with that. That's a good thing."

Obama praises McCain for working on immigration reform but criticizes him for backing away from his own record during the GOP primary.

During a January debate in California, McCain repeatedly refused to say whether he'd vote for his own proposal if it came to the Senate floor. He said Americans made clear they want the border secured first, before other measures are taken.

"I want to be fair here, John McCain bucked a bunch of his party. ... And I thought that was great," Obama said Thursday in Virginia. "Unfortunately when he started running for the presidency and he was taking some incoming from his party in the primary, he announced that he wouldn't even vote for the bill that he had drafted. ... That can't give you confidence that he is going to be serious about that issue.

"I will be, because I think it's a problem we'll have to solve."

Obama made a similar charge June 28 when both candidates addressed the National Association of Latino Elected and Appointed Officials in Washington, D.C. The two candidates addressed the League of United Latin American Citizens on Tuesday.

Janet Murguía, president of the National Council of La Raza, gave both senators credit for pushing immigration reform, but in a statement Friday called on them to rein in what the organization termed "offensive and charged rhetoric on immigration" in congressional campaigns.

"Hate has hijacked the immigration debate," Murguía said in a statement. "As the leaders of their respective parties, I challenge Senators Obama and McCain not to look the other way while others stoop to demagoguery. I urge them in the strongest possible terms to confront inflammatory anti-immigrant language and images when members of their party seek to use them as campaign tactics.

"I ask them to lead the country in elevating the tone in this badly needed policy debate."

McCain is looking to build on the gains President Bush made with Hispanic voters in 2004, when he earned 40 percent of the Hispanic vote -- a record for a Republican presidential candidate.

Though Obama consistently lost Hispanics to Hillary Clinton during the Democratic primary race, he is leading McCain by a wide margin so far.

A recent AP-Yahoo News poll showed Obama with 47 percent support among Hispanics, compared with 22 percent for McCain. Twenty-six percent were undecided.

FOX News' Bonney Kapp and The Associated Press contributed to this report.