Republican National Committee Chairman Ken Mehlman urged his party Thursday to oppose rising anti-immigrant sentiments in the debate over border security and illegal immigration, suggesting that the GOP risks being on the wrong side of history and electoral politics alike if it embraces an exclusionary message.

Appearing before the Republican Governors Association, Mehlman waded into an issue that political analysts say threatens to rip apart the Republican coalition and inflict long-term damage to the party's hopes of expanding its appeal to Latinos and other minorities. A top political hand to President Bush, Mehlman followed the White House lead in treading a middle path on the issue: He issued a strong call for tougher enforcement of immigration laws but extolled the contributions of immigrants and denounced those who have sought to close the country to foreigners.

"Throughout our history, there have always been Americans who believed that coming to these shores was a right reserved only for them and their ancestors, but not for others," Mehlman said. Citing Republicans and Democrats from earlier eras who had expressed anti-immigrant prejudice, he added: "Ladies and gentlemen, that was wrong then and those who argue that now are wrong today."

Mehlman said after the speech that he was not aiming his remarks at any particular person or politician. But his message offered a counterweight to the views of many conservatives, led by Rep. Tom Tancredo (R-Colo.), who have warned that illegal immigration is damaging to the nation.

The party chairman spoke three days after Bush traveled to the Mexican border to highlight his determination to strengthen security along the country's southern flank. But the president also emphasized his support for a guest-worker program that would provide legal status to many temporary workers. Tancredo called that tantamount to amnesty for illegal immigrants.

Few states illustrate more vividly than California the double-edged nature of the problem that immigration presents to the Republican Party. In 1994, then-Gov. Pete Wilson (R), responding to growing voter resentment over the tide of illegal immigration at a time of economic recession, sought reelection on a platform strongly opposing illegal immigration. Wilson helped engineer a ballot initiative, Proposition 187, that sought to eliminate government assistance for illegal and some legal immigrants.

The strategy helped Wilson survive for a second term, but proved disastrous for the Republican Party in the state. The 1996 election produced a surge in participation by Latinos, raising their share of those who turned out to vote by roughly a third, with Democrats winning 70 percent of their votes.

With Latinos now the fastest-growing segment of the population, Republicans can ill afford to offend them with immigration policies that are seen as punitive. GOP strategist Mike Murphy, who participated in a panel discussion after Mehlman's speech, noted that in California, a politician now can win 70 percent of the white vote and still lose an election because of the state's growing diversity.

Bush long has resisted the most vociferous anti-immigration rhetoric in his party. His political team has focused relentlessly on reaching out to the Hispanic community, and his share of the Latino vote grew measurably between 2000 and 2004.

In the face of growing resentment among citizens in border and neighboring states that the federal government has lost control of border security, Bush and other politicians now are under pressure to respond with tougher immigration policies. But Republican pollster Bill McIntuff told the governors meeting that the party must respond, but with language that does not sound exclusionary. "We have to have the right policy and soft language," he said.

"America is a nation of immigrants and America is a nation of laws, and we must remember the 'and' between the two," Mehlman told the governors. Portraying most immigrants as hardworking and law-abiding, Mehlman said that Bush recognizes that "family values don't stop at the Rio Grande."