Reporting from Washington - With the healthcare battle still unfinished, the Obama administration has been laying plans to take up an issue that could prove even more divisive -- a major overhaul of the nation's immigration system.

Senior White House aides privately have assured Latino activists that the president will back legislation next year to provide a path to citizenship for the estimated 12 million illegal immigrants living in the United States.

In a recent conference call with proponents, White House Deputy Chief of Staff Jim Messina, political director Patrick Gaspard and others delivered the message that the White House was committed to seeing a substantial immigration bill pass and wanted to make sure allies were prepared for the fight.

In addition to the citizenship provision, the emerging plan will emphasize efforts to secure U.S. borders against those trying to cross illegally. But that two-track approach was rejected repeatedly in the past by Republicans and other critics who insist that a border crackdown must demonstrate its effectiveness before any action on citizenship is considered.

Whatever proposal Obama puts forward will probably meet equally determined opposition. Another complication is the calendar: Midterm elections are in November, and polls show that the public is more worried about joblessness and the fragile economy than anything else.

So embracing an immigration bill is a gamble for the White House, which already has a packed agenda for 2010: economic recovery, global warming legislation and tougher regulation of financial institutions.

No matter what the environment, immigration is a tough sell, said Democratic pollster Geoff Garin.

"We know from a lot of experience that immigration reform has been and can be a very polarizing issue. There are heated differences about whether there ought to be some kind of pathway to citizenship for people who entered the country illegally," he said.

"And my sense from the public-opinion research is people care more about vindicating their position than they do about getting the issue solved."

Even so, the White House apparently has decided to press ahead.

In an effort to enlist the kind of business support that helped drive its healthcare initiative, for example, administration officials have reached out to the National Restaurant Assn., which represents an industry that employs thousands of immigrants. Earlier this year, the new head of the association, Dawn Sweeney, met with Cecilia Muñoz, a White House aide involved in the issue, and expressed interest in cooperating.

"It's an extremely important issue for our members," said Sweeney, whose group could exert grass-roots pressure on lawmakers.

As a candidate, Obama vowed to take up immigration during his first year in office. That deadline will come and go. Further delay could anger Latino voters, who came out in force for the president and congressional Democrats in 2008.

No one anticipates that a core element of the Democratic base will defect to the Republican Party in November. But even a significant drop in turnout -- which often happens in nonpresidential elections -- could frustrate Democratic efforts to preserve their congressional majority.

"The bulk of the people needing immigration reform are Latino," said Rep. Raul M. Grijalva (D-Ariz.). "There's a level of disenchantment about where we're going. . . . And if you don't give the Latino community a reason to participate [in the elections], you weaken your base even more."

For an immigration bill to have a realistic shot of passing next year, political analysts said, the particulars would have to be agreed upon by the spring. A delay would increase the likelihood of the issue getting derailed by the November elections.

Henry G. Cisneros, a Cabinet secretary in the Clinton administration who took part in the recent immigration conference call with the Obama White House, said: "It gets much more difficult as the year goes along. So everyone has to be very sober about the prospects. But the president and congressional leadership understand it's important to start the ball rolling."

An immigration bill was introduced in the House earlier in the month, and Sen. Charles E. Schumer (D-N.Y.), who chairs a subcommittee on immigration, is heading the effort to cobble together a bipartisan coalition in the Senate.

But Democrats may not have a lock on one prominent Republican who has worked in the past to revamp the immigration system: Arizona Sen. John McCain.

McCain backed President George W. Bush's failed attempt to overhaul immigration in his second term. But he has not committed to supporting the Obama bill, saying he worried the president would not endorse a temporary guest-worker program.

Organized labor, an important part of the Democratic base, has voiced opposition to a guest-worker program under which more immigrants could enter the country on a temporary basis. Critics argue that there is no effective system for ensuring that such workers will leave the country when their permits expire.

"From everything that we hear right now, the temporary guest-worker program won't be addressed in immigration reform. And unless that is an essential part of the reform program, it's something that Sen. McCain can't work on," said Brooke Buchanan, a spokeswoman for the Arizona lawmaker.

The White House would not reveal its position on the guest-worker issue.

Should an immigration bill gain traction, White House Chief of Staff Rahm Emanuel would probably be a central player in the negotiations.

As an aide to President Clinton, Emanuel co-wrote a memo on the political dynamics of immigration. He and Ron Klain, now the top aide to Vice President Joe Biden, wrote in 1994: "We must be seen as taking proper, forceful steps to seriously address the immigration problem without alienating the Hispanic and civil rights constituencies.

"Our goal is not to outdo the Republicans, rather to use our achievements and proposals to prevent them from using this as a wedge issue against us."

The former head of the Immigration and Naturalization Service, Doris Meissner, recalled that Emanuel once phoned and berated her over a news story about lax border enforcement in Arizona.

"This kind of press is killing us," Meissner quoted Emanuel as saying. During the call, he instructed her to send border agents to the area immediately. "He had no authority whatsoever to give me orders," Meissner said.

But Emanuel was constantly pressing his colleagues in the Clinton White House to push what he termed a "balanced" immigration policy -- including enforcement and stepped-up grants of citizenship.