WASHINGTON, (By David D. Kirkpatrick, NYTimes) March 30, 2006 — The battle among Republicans over immigration policy and border security is threatening to undercut a decade-long effort by President Bush and his party to court Hispanic voters, just as both parties are gearing up for the 2006 elections.

"I believe the Republican Party has hurt itself already," said the Rev. Luis Cortes, a Philadelphia pastor close to President Bush and the leader of a national organization of Hispanic Protestant clergy members, saying he delivered that message to the president last week in a meeting at the White House.

To underscore the contested allegiance of Hispanic voters, Mr. Cortes said, he also took a delegation of Hispanic ministers to meet with the leaders of both parties last week, including what he called a productive discussion with Howard Dean, the Democratic chairman.

The immigration and security debate, which has sparked huge demonstrations in recent days by Hispanic residents of cities around the country, comes at a crucial moment for both parties.

Over the last three national elections, persistent appeals by Mr. Bush and other Republican leaders have helped double their party's share of the Hispanic vote, to more than 40 percent in 2004 from about 20 percent in 1996. As a result, Democrats can no longer rely on the country's 42 million Hispanic residents as a natural part of their base.

In a lunch meeting of Senate Republicans this week, Senator Mel Martinez of Florida, the only Hispanic Republican in the Senate, gave his colleagues a stern warning. "This is the first issue that, in my mind, has absolutely galvanized the Latino community in America like no other," Mr. Martinez said he told them.

The anger among Hispanics has continued even as the Senate Judiciary Committee proposed a bill this week that would allow illegal immigrants a way to become citizens. The backlash was aggravated, Mr. Martinez said in an interview, by a Republican plan to crack down on illegal immigrants that the House approved last year.

The outcome remains to be seen. Speaker J. Dennis Hastert said on Wednesday that he recognized the need for a guest-worker program, opening the door to a possible compromise on fiercely debated immigration legislation.

Democrats see an opportunity to "show Hispanics who their real friends are," as Senator Charles E. Schumer of New York, chairman of the Democratic Senatorial Campaign Committee, put it.

But the issue is a delicate matter for Democrats as well. Polls show large majorities of the public both support tighter borders as a matter of national security, and oppose amnesty for illegal immigrants. Many working-class Democrats resent what they see as a continuing influx of cheap labor.

The stakes are enormous because Hispanics now account for one of every eight United States residents, and for about half the recent growth in the country's population. Although Hispanics cast just 6 percent of the votes in the 2004 elections, birth rates promise an imminent explosion in the number of eligible voters.

"There is a big demographic wave of Hispanic kids who are native born who will be turning 18 in even greater numbers over the next three, four and five election cycles," Roberto Suro, director of the nonpartisan Pew Hispanic Center, said.

Nowhere is the immigration debate more heated than Arizona, where about 28 percent of the population is Hispanic and where Senator Jon Kyl, a Republican sponsor of an immigration bill, faces what could be a difficult race for re-election. Both Mr. Kyl and his Democratic challenger, Jim Pederson, have hired Hispanics or Hispanic-dominated firms to manage their campaigns.

A mostly Hispanic crowd of about 20,000 gathered outside Mr. Kyl's office last weekend to protest criminal penalties against illegal immigrants that were in the House Republican bill, even though Mr. Kyl's proposal does not include the measure.

Mario E. Diaz, the campaign manager for Mr. Pederson, faulted Mr. Kyl's proposal, which would require illegal immigrants or future temporary workers to return to their countries before becoming eligible for legal status in the United States.

"Speaking the language that Kyl does, which is round them up and deport them, is offensive and disgusting to the Latino community," Mr. Diaz said.

Mr. Kyl, for his part, accused Democrats of race-baiting by painting all Republicans as anti-Hispanic, a practice he said most Hispanics resent. But the senator also acknowledged some fears that the immigration debate could repel Hispanic voters. He added, "I would hope that some of our colleagues who don't have much of a Hispanic population in their states would at least defer to those of us who do."

Pollsters from each party say Hispanics, like other groups, typically rank immigration lower in importance than other issues, especially education. But they respond strongly when they believe the rhetoric surrounding the debate demonizes immigrants or Hispanics, as they did when Gov. Pete Wilson of California, a Republican, backed a 1994 initiative to exclude illegal immigrants from public schools and services.

Many analysts say the backlash from Hispanics wrecked the California Republican party for a decade.

As governor of Texas, Mr. Bush opposed such measures, and pushed Republicans to woo Hispanics.

Last week, Sergio Bendixen, a pollster for the Democratic Senatorial Campaign Committee, released a rare multilingual poll in which 76 percent of legal Latin American immigrants said they believed anti-immigrant sentiment was on the rise. A majority of immigrants said they believed the immigration debate was unfair and misinformed.

But Ken Mehlman, chairman of the Republican National Committee, dismissed such concerns. Mr. Mehlman said the party's image was defined by President Bush, who supports a temporary-worker program and has repeatedly urged Republicans to avoid inflammatory rhetoric.

"In an emotional debate like this," Mr. Mehlman said, "people need to lower their energy and remember that ultimately the goal is something that is consistent with being a nation of laws and a nation of immigrants."

Danny Diaz, a spokesman for the Republican Party, said it had pushed ahead on recruitment of Hispanic candidates and voters. He noted that Mr. Mehlman had appeared frequently at events with Hispanic groups, hitting classic Republican themes about lower taxes and traditional values. A particular focus has been Hispanic churchgoers and pastors like Mr. Cortes, who receives money from Mr. Bush's religion-based social services initiative.

Democrats say that Mr. Bush's success with Hispanics has not gone unnoticed. Democratic leaders in Congress have expanded their Spanish-language communications, and after 2004 the Democratic Party vowed to stop relying on payments to Hispanic groups and organizations to help turn out Hispanic voters.

"How can you spend your money on get-out-the-vote when you are beginning to lose your market share?" Mr. Bendixen said. "But Democrats had no experience in campaigning for the hearts and minds of Hispanic voters. They treated them like black voters who they just needed to get out to the polls."

Still, both sides say it is the tenor and ultimate outcome of the immigration debate that may give the Democrats their best opportunity to attract Hispanic voters.

Senator Martinez, a Cuban immigrant who delivered part of a Senate speech in Spanish a few months ago, alluded to the nervousness among Hispanics when he was asked whether he would do the same again in the debate on immigration. "I am about to be sent back as it is," he said, joking. "I better be careful."