DALLAS ((By Annabelle Garay and Suzanne Gamboa, AP) March 3, 2008 — American-born Manuel Rendon came of legal age in the midst of rallies around the country for immigration reform and quickly registered to vote.

"Once I turned 18, I knew that was the one way to have my voice heard and to really make an impact. So it wasn't just my right, it was my duty," said Rendon, the son of Mexican immigrants.

For years, Hispanics have lagged behind other voters in their political clout, in part because so many of them were under 18.

But now, 400,000 U.S.-born Hispanics a year are joining the voting-age population by turning 18. More than 5 million Hispanic citizens, either U.S.-born or naturalized, were ages 18 to 29 as of September 2007, according to the Pew Hispanic Center.

The power of that fast-growing slice of the Hispanic vote may soon be put to the test in Texas, where Democratic presidential candidates Hillary Rodham Clinton and Barack Obama are competing fiercely for the support of Hispanic voters in the state's March 4 Democratic primary.

About 20 percent, of 2.6 million, registered voters in Texas have Hispanic surnames, and about a third of the state's eligible Hispanic voters are 18 to 29.

"If they turn out in bigger numbers than they have in the past, it could be a real turning point. It's this very large and growing untapped pool," said Roberto Suro, a founder of the Pew Hispanic Center and a journalism professor at the University of Southern California's Annenberg School for Communication.

Three other states hold primaries Tuesday. Ohio has a large cache of delegates, but Hispanics comprise only 1.5 percent of the electorate there; 5.6 percent of eligible voters are Hispanic in Rhode Island, and 0.6 percent in Vermont.

Nationally, the young Hispanic population is growing so quickly that older community organizations are having a hard time keeping up, said Maria Teresa Petersen, executive director of Voto Hispanic, a nonpartisan group.

While the debate over immigration is driving some young Hispanics to the polls, their interests extend to other issues, such as education, the war and the economy. But candidates who rely on such traditional political tools as Spanish-language ads to reach Hispanics may be missing many young Hispanic voters who get their political information in English or in both languages, Petersen said.

"When I travel cross-country and go to conferences to talk to young people, I tell them: 'Don't forget. Yes, you are Cuban, Mexican or Peruvian, but don't forget you're also American.' They get off their seats and start clapping. No one is recognizing their Americanness, and that's what these kids desperately want to demonstrate," Petersen said.

Voto Hispanic is trying to reach young voters through the Web and text messages to get them to the polls. About 78 percent of English-dominant Hispanics are online, Pew Hispanic reported last year. The study also found that about 49 percent of Hispanic cell phone users send and receive text messages.

The group plans to text get-out-the-vote messages to young Hispanics.

It also produced a Web-based mock "telenovela," or soap opera, in English with Declare Yourself, another youth get-out-the-vote group. The telenovela stars actors Wilmer Valderrama, from "That '70s Show," movie actress Rosario Dawson, Tony Plana of "Ugly Betty" and others.

"If they are Hispanic, they think it's funny. It cracks them up. The folks that aren't Hispanic said, 'I don't get it.' We definitely hit a cultural midsection," Petersen said.

Some young Hispanics, like Raul Delgado, 26, who voted in California's Feb. 5 primary for Clinton, don't have to be persuaded to vote. The longshoreman and former Marine said his family's tradition of voting and discussing politics at their many get-togethers led him to register soon after turning 18.

"Growing up, you hear how important it is to get your vote in," said Delgado, whose father immigrated from Mexico as a teenager. "Hopefully it will make you be heard."

In Texas, Obama has won the coveted endorsement of the Mexican American Democrats and held rallies at several universities. Clinton has been campaigning primarily along the Texas-Mexico border, including on the campuses of the University of Texas-Brownsville and UT-Pan American.

Republicans also go to the polls March 4 in Texas. GOP nominee-in-waiting John McCain held a town hall meeting at a military-related site in San Antonio on Wednesday.

In that heavily Hispanic city, Anna Urrabazo, 28, is undecided in 2008 but voted for President Bush in 2004. The daughter of U.S.-born Hispanics, she said Spanish-language campaigning "doesn't pick up on my vote."

"That type of campaigning, they try to influence the Hispanic or African-American race. I think that's all for show. I personally think maybe they shouldn't use that. It's more the issues that affect us, the middle class, not images," she said.

Groups seeking to increase voter participation are hoping the unusually high level of interest in the 2008 campaign will spur young Hispanics to vote. Their participation has held steady at 23 percent since 2000, said Richard Fry, a senior researcher at the Pew Hispanic Center.

"One barrier they don't have to deal with is citizenship, but that doesn't turn them into voters," Fry said.

That's where Rendon, 20, and others are stepping in.

Rendon, who works two jobs and attends community college in Collin County outside Dallas, has gone looking for voters. Last year, he and other student members of the League of United Latin American Citizens took voter registration cards to Dallas public high schools, where Hispanics are the majority. They registered about 2,000 high school seniors and continue to prod them to vote.

And even though Rendon acknowledges there are more ways than ever to reach young voters, he still has work to do urging them to the polls.