Even as Congress is consumed with fiscal cliff negotiations, lobbyists and activists on all sides of the immigration debate are mobilizing their grass roots, staking out policy turf and gearing up for a huge push next year.

Advocates of overhauling the nation’s immigration laws say their messaging includes entreaties to Congress to keep any bill clean. The fear is the legislation could become a “Christmas tree,” larded up with enough pet projects and controversial amendments to sink it. Such a scenario is not lost on overhaul opponents, either.

“Anybody that comes forward with non- germane measures or something that is intended to delay and frustrate the process, we are going to keep our eyes on them,” said Eliseo Medina, secretary-treasurer of the Service Employees International Union, which supports a path to citizenship for illegal immigrants. “They’re buying themselves a lot of trouble in the next election if they stand in the way of real reform.”

A comprehensive rewrite of immigration laws appears to be one of the few opportunities for bipartisan comity in the next Congress. And it’s an issue that many Republicans say their party must take on, especially after Mitt Romney lost the Latino vote by a huge margin.

Medina said his outreach to the Latino community is full time — with ongoing operations in such states as Colorado, Nevada, Florida, Texas and California. The upcoming campaign will include rallies, one-on-one meetings with members of Congress and more specifics that will be announced within 45 days, he said.

Advocates from different sides of the issue agree that an immigration rewrite will likely be a Senate-driven process requiring the chamber’s leaders to devise a legislative framework and stick to it. Senators such as Republican Lindsey Graham of South Carolina and Democrat Charles E. Schumer of New York are among the players that K Street plans to court.

“Managers of the legislation on both sides of the aisle in both chambers will be … keeping a wary eye out for extraneous amendments that could potentially bring the bill down,” said Chuck Merin, a veteran lobbyist with Prime Policy Group whose restaurant and travel clients have a stake in the outcome.

The starting point should be finding a path to citizenship for undocumented workers already here, according to many rewrite advocates such as Medina. Though some Republicans think that could be a nonstarter, pressure from the evangelical community could yet garner GOP support.

Randy Johnson, who handles immigration for the U.S. Chamber of Commerce, is busy laying the groundwork with the business group’s members around the country. “I’ve been doing this over a decade, and I feel more optimistic now than I ever have,” he said. “You reap what you sow.”

The group supports increased border security, a civil fine for those who entered the country illegally and tougher penalties for businesses that hire undocumented employees. Johnson said employers need more temporary workers to fill slots.

But Julie Kirchner, executive director of the Federation for American Immigration Reform, which strongly opposes citizenship for illegal immigrants, isn’t buying Johnson’s message. With unemployment at roughly 8 percent, she said, finding workers isn’t the problem. And FAIR activists are making personal calls to their networks urging voters to press their case with lawmakers.

An immigration overhaul could attract non-germane amendments or ones expressly designed to derail the measure. A 2007 overhaul of immigration laws drew hundreds of proposed amendments and was eventually shelved after Senate leaders couldn’t come to agreement.

“I can guarantee you, there will be people pushing every variation of immigration reform legislation,” Kirchner said. “We’ll see what kind of behemoth this turns into.”

But Matthew Soerens, U.S. church training specialist for World Relief, the humanitarian arm of the National Association of Evangelicals, said that more conservative-voting church- goers are beginning to view immigration in a new light, as their pastors and leaders have called for immigration reform.

“More and more evangelicals in the pews are asking what a biblical response to immigration issues looks like,” he said, adding that the Bible preaches respect for the rule of law, as well as treating immigrants with compassion.

His organization supports toughening border control, making it easier to immigrate legally and keep families together and setting fines for those who entered the U.S. illegally and then putting them on a path toward citizenship.

Soerens’ evangelical organization has ramped up its grass-roots outreach since the elections and plans to distribute bookmarks with references to 40 relevant biblical passages that it urges parishioners to read over 40 days.

But legislation addressing the already politically thorny issue may morph into a crucible for other socially charged topics.

Kevin Appleby, director of migration policy for the United States Conference of Catholic Bishops, said his group is ginning up its grass roots and plans to work both sides of the aisle in support of a bill. “There is a moral argument to be made,” he said. “We have 11 million undocumented people living in the shadows, a lot of them work in this country as a permanent underclass. That’s not the American way.”

But Appleby will keep his eyes out for a policy that would create an immigration category for relatives of same-sex families, something the bishops oppose. That would “only complicate the situation. It’s an explosive mix,” he said.