Updated: 5:05 p.m.

Despite renewed interest in tackling comprehensive immigration reform this year, Democratic and Republican aides in the House and Senate said prospects for serious action on the thorny issue remain uncertain at best.

Aides also warned that the complexities and politically toxic nature of immigration reform would almost certainly force one or more of President Barack Obama’s top-line agenda items off the table for the year.

“How do we let more immigrants in, or legalize people, when Americans need jobs?— a senior House Democratic aide said. “Putting aside how horrific the vote is for some people anyway, the politics of this have only gotten worse.—

The aide said immigration reform ranks last among the White House’s highest priorities, after major overhauls of health care, energy, education, financial regulations and fiscal responsibility. “I don’t think the White House is going to go to the mat for immigration,— the aide said.

A senior Senate aide agreed, arguing that despite pressure from the Congressional Hispanic Caucus and some elements of his own administration, it will be nearly impossible for Obama to complete work on his top priorities if immigration is thrown into the mix.

“With all of Obama’s other initiatives that have been stated, this is going to be a huge list,— the aide said, adding that the Senate is already expected to address energy, health care reform, the annual appropriations process and an equally controversial “card check— labor bill before the end of the year.

But White House Press Secretary Robert Gibbs said Thursday that Obama does not expect to complete comprehensive immigration reform this year.

“Obviously, there are a lot of things on his plate and a lot of pressing issues related to the economy,— Gibbs said. “I don’t think that he expects that it will be done this year.—

Gibbs said that Obama had promised during the campaign to “begin— the process on immigration reform his first year and that he is following through, adding that Obama is committed to acting on the issue. However, Gibbs also acknowledged that passing comprehensive immigration reform will be difficult.

And aides added that when that list includes the potential for another supplemental war spending bill, the host of executive and judiciary nominations, and the continuing focus on the economy, it will be almost impossible for either chamber to seriously consider immigration reform before next year unless Obama is willing to drop an issue, such as energy legislation.

Additionally, political realities would likely dictate that Speaker Nancy Pelosi (D-Calif.) — who must contend with the conservative Blue Dog Coalition and a number of Members from traditionally Republican districts — would not take up the bill before the Senate, which would push back action significantly, Democrats said. In fact, a senior House Democratic aide said it is “likely— the Senate will move first on the issue.

A story in the New York Times on Thursday quoting White House Director of Intergovernmental Affairs Cecilia Muñoz saying Obama would push for legislation this year sent Democratic lawmakers scrambling.

Publicly, Democrats said they have begun conversations on the issue with the White House and hope to move legislation this fall.

Senate Majority Leader Harry Reid (D-Nev.) “expects to take a bill to the floor sometime this fall,— Reid spokesman Jim Manley said, adding that Sen. Charles Schumer (D-N.Y.), who chairs the Judiciary Subcommittee on Immigration, Refugees and Border Security, would lead the charge.

In a statement, Schumer said he believes there is a chance to reform immigration laws this year.

“We must solve the immigration issue and we can, even in these difficult economic times. I believe there is a real chance of passing comprehensive reform this year, and the Senate panel on immigration will begin a series of meetings and hearings later this month with an eye towards meeting that goal,— Schumer said.

But privately, Democrats said the statement by Muñoz — whose office does not have a direct role in immigration issues — took Capitol Hill by surprise, and that there has been no substantive discussions on immigration reform to date.

A potentially significant issue for the administration could be opposition from Republicans and moderate “red state— Democrats both in the House and the Senate.

Rep. Steve King (R-Iowa), a vocal critic, harshly criticized the idea of taking up immigration reform. In a statement, King seized on the continuing economic crisis as a key reason for opposing legislation.

“In our current economic crisis, Americans cannot afford to lose more jobs to illegal workers. With more than 12 million illegal aliens living in the United States and over 7.7 million of those illegal aliens working in the United States, America cannot afford to grant amnesty to those that have broken the rule of law. American workers are depending on President Obama to protect their jobs from those in America illegally,— King said.

A second Senate Democratic aide acknowledged that if the administration actually does try to take up the issue this year, Democrats can expect more of the same, and questioned the wisdom of pursuing the bill given the economic climate. The aide warned that the legislation could give Republicans the ability to say, “We’re giving your jobs to illegal immigrants.—

Indeed, Republicans said the administration shouldn’t expect to find supporters within their ranks, particularly in the Senate, if Obama simply drafts his own legislation without input from the GOP.

One GOP leadership source noted that for Republicans, the politics of immigration reform have changed significantly since 2007, the last time Congress made an effort on a comprehensive immigration bill.

At that point, a number of Senate Republicans opted to back a push by Sen. John McCain (R-Ariz.), Senate Democrats and the Bush administration to pass a bill, arguing it might be the best chance for an acceptable bill, particularly if they lost badly during the 2008 election.

“There was a sentiment amongst Republicans in the last go-round that a reason to support a comprehensive package was that if we did lose seats and the presidency in the next election, we were going to get a significantly worse package,— a GOP leadership aide explained.

Additionally, this source said it is unlikely McCain will reprise his role as the GOP’s lead negotiator on immigration. For instance, during a meeting with Latino business leaders, McCain made it clear that if comprehensive reform is going to move, the White House will have to take the lead. McCain “made it clear that Obama is going to have to lead on this,— a source familiar with the meeting said.

But for now, Senate GOP leaders appeared content to lend at least nominal support for the idea of immigration reform.

National Republican Senatorial Committee Chairman John Cornyn (Texas) applauded the administration’s commitment to comprehensive reform.

“I applaud President Obama’s commitment to addressing comprehensive immigration reform this year, and stand ready to work with him to produce a product that represents the best interests of America, including respect for the rule of law, national security and economic security,— Cornyn said in a statement.

Jen Bendery and Tory Newmyer contributed to this report.