By JULIA PRESTON

On the stump, Senator Barack Obama and Senator John McCain rarely talk about immigration, and it was never raised in their three debates.

Yet as this thorny issue has receded from the presidential campaign, the two candidates continue to refine their approach to it — especially in regards to illegal immigration, the most politically sensitive piece of the equation.

Mr. Obama, the Democratic nominee, has hardened his tone on how to deal with illegal immigrants, while Mr. McCain, the Republican nominee, has made immigration enforcement a priority, a position in line with the Bush administration’s. Both candidates are responding to the anger many Americans feel about uncontrolled illegal immigration, including working-class voters whom Mr. McCain and Mr. Obama are trying to attract in the final days of the campaign.

Because of persisting political rifts and a crush of priorities related to reviving the economy and unwinding the Iraq war, advisers to the campaigns say it is increasingly unlikely that either candidate would propose to Congress an overhaul of the immigration system during the first year in office, something both Mr. McCain and Mr. Obama had pledged to do.

On the assumption that immigration legislation “is not likely to be the first thing out of the box” for the new president, Doris Meissner, who was commissioner of the immigration service under President Bill Clinton, said she was working with a bipartisan group of experts to identify changes that the new president could make without Congress.

“The reforms we need to put in place are so sweeping and the political environment is so hostile to consensus, I think we will be in a phase of longer-term building of public understanding,” said Ms. Meissner, a senior fellow at the Migration Policy Institute, a research group in Washington.

Both Mr. Obama and Mr. McCain continue to support legislation that would include a path to legal status for the estimated 12 million illegal immigrants in the country.

As a result, groups that oppose legal status for illegal immigrants, who mobilized a wildfire movement of largely Republican voters against a comprehensive immigration bill last year, are sitting out the presidential race. Instead, they are focusing on Senate and House races, where they hope to stop the Democrats from winning large majorities.

“We’re going to have an incredibly bad White House, so we’re in for some tough defensive battles,” said Roy Beck, president of NumbersUSA, which favors reduced immigration. “We have to make sure we’ve got at least 41 senators so we can block any Obama or McCain amnesty.”

Seeking to broaden support for legalization, Mr. Obama embraces new law-and-order language adopted in the Democratic Party platform at the convention. Although Americans are “welcoming and generous,” the platform states, “those who enter our country’s borders illegally, and those who employ them, disrespect the rule of law.” Instead of the Democrats’ emphasis, as recently as last year, on integrating illegal immigrants into society, the platform says, “We must require them to come out of the shadows and get right with the law.”

Heather Higginbottom, the Obama campaign’s director for policy, said Mr. Obama had not altered his basic views. If elected, Mr. Obama would insist that illegal immigrants pay back taxes and fines, learn English and go to the back of the immigration line to become legal.

For Mr. McCain, there has been a sharper turn from the past. He was unable to stop the Republican Party from adopting a platform at the September convention that directly rejected his support for legalization. “We oppose amnesty,” the platform states, describing “the American people’s rejection of en masse legalizations” as “especially appropriate.”

Some Republicans have not forgiven Mr. McCain for joining Senator Edward M. Kennedy, Democrat of Massachusetts, to write a bill, known as comprehensive immigration reform, which passed the Senate in 2006. Mr. McCain stayed on the sidelines last year as a version of that bill stalled in Congress. Then, under pressure from rivals in the Republican primaries, Mr. McCain said early this year that he would not vote for that bill if it came up again.

He has supported the Bush administration’s aggressive enforcement campaign against illegal immigration, calling it a necessary first step to persuading Americans to accept any legalization program. In recent weeks his campaign has avoided the term “path to citizenship” to describe the option Mr. McCain would offer illegal immigrants, saying only that he would deal with them in a humane way.

The McCain campaign is hoping that his differences with the Republican Party will help to reinforce his image as a maverick, especially among Hispanic voters. One of his television advertisements in Spanish shows Mr. McCain speaking of illegal immigrants as “God’s children,” as Representative Tom Tancredo of Colorado, the Republicans’ most outspoken foe of illegal immigrants, looks on, scowling.

“Senator McCain risked his own political career to get a bill in the Senate that would benefit Latinos,” said César Martínez, a producer of the McCain advertisements in Spanish.

Obama supporters say they do not mind his campaign’s silences, since they are confident he remains committed to an overhaul including legalization, and debate has often proved polarizing.

“We feel very comfortable with where he stands,” said Eliseo Medina, international executive vice president of the Service Employees International Union, who has been barnstorming for Mr. Obama. “We do not have to have it repeated to us over and over again.”

Ms. Higginbottom, the Obama policy adviser, acknowledged that high unemployment in coming months could make an immigration overhaul a harder sell but said Mr. Obama would argue that American workers would benefit if millions of unauthorized immigrant workers, currently vulnerable to exploitation, gained their labor rights.

While the candidates have skirted the immigration issue in speeches and town-hall-style- meetings, they are clashing head on over it in the Spanish language media, in negative advertisements that have played heavily in swing states with growing numbers of Hispanic voters like Colorado, Florida, Nevada and New Mexico.

In those advertisements, Mr. McCain and Mr. Obama each tries to show that the other was less consistent in supporting legislation to change the system, including provisions to legalize illegal immigrants.