San Antonio Mayor Julian Castro (with his brother, Texas Democratic Rep. Joaquin Castro behind him) testifies on Capitol Hill on Feb. 5 before the House Judiciary Committee hearing on immigration. (Susan Walsh/AP)

Congress’ formal legislative debate on immigration opened Tuesday with a hearing in the House, where partisan cracks on the difficult issue emerged almost immediately.

Democrats on the panel focused on the need for a comprehensive overhaul that would expand legal avenues for immigration, improve enforcement of new laws and a path to eventual citizenship for the estimated 11 million people living in the country illegally.

But a number of Republicans who sit on the Judiciary Committee, a key gateway to any new immigration law, questioned whether there might be a middle ground between deportation of those here illegally — long the goal of many in their party — and extending citizenship.

The issue is quickly emerging as a flash point in the debate.

“How do we avoid creating an incentive for people to continue to come here?” said Rep. Blake Farenthold (R-Tex.) of systems that would eventually afford full citizenship to those who broke immigration laws. “That’s the big stumbling point.”

Immigrants living in and leaving the United States

San Antonio Mayor Julian Castro (D), the star witness of the first of two panels of witnesses who testified before the hearing, told Farenthold that better enforcement of visa laws and verification by employers of their workers’ legal status would help. He insisted, however, that full citizenship needs to be an option.

“I just cannot imagine an America where we assign these folks to an underclass status. In other words, we would be telling them, you will never become a citizen of the United States,” he said.

“How is that a compromise?” asked Rep. Trey Gowdy (R-S.C.), who chairs the key judiciary subcommittee charged with vetting immigration bills, discussing the same point earlier in the hearing.

The hearing was briefly interrupted by a knot of protesters shouting “undocumented and unafraid!”

But it was a largely muted discussion of what has traditionally been one of politics’ most emotional issues, a sign of a desire by Republican leaders to find some way to address the immigration issue amid fears that the party has alienated a growing number of Hispanic voters with its hard-line stance.

The new session of Congress opened in January, and House Judiciary Committee Chairman Bob Goodlatte (R-Va.) chose the immigration issue for his panel’s first hearing as a sign of commitment on the issue. He promised that Tuesday’s session was the first of many to come.

“This issue is too complex and too important to not examine each piece in detail,” he said. “We can’t rush to judgment.”

The debate comes as President Obama has launched a new push to encourage Congress to fix what he sees as a broken system. Obama met with labor leaders and immigration advocates Tuesday morning at the White House and was scheduled to meet with business leaders in the afternoon.

Last week, a bipartisan group of eight senators advanced a statement of principles to guide a comprehensive effort. It called for allowing illegal immigrants to pay a fine and back taxes and quickly achieve legal status. It said that they would also have eventual access to green cards, which allow permanent residency and eventual citizenship. However, it tied citizenship to improved enforcement and border security.

At the House hearing, some Republicans also voiced skepticism over a single overhaul of the law — indicating that they would prefer to focus piecemeal on different areas of the code. Specifically, they said they were open to providing new visas to high-skill workers, long a Republican priority that immigrant advocates fear could replace a broader strategy that also addresses what to do with those already here.

And the panel expressed disagreement over whether a temporary guest worker program should be created to allow businesses to import workers. Unions and some advocates believe such workers undercut U.S. wages. Some Republicans think they offer a way to extend temporary legal status to agricultural workers.

Rep. Raul R. Labrador (R-Idaho) told one panel member, who chaired a commission that 15 years ago advocated against a guest worker program, that the position left him “dumbfounded.”

Immigration advocates also expressed disappointment with the House hearing Tuesday, saying citizenship for those now working in the country illegally is key to avoiding the creation of a permanent group of second-class temporary workers.

“We’re frankly sad that in this day and age and in this moment, there are still some members who are focused on sowing division and mischaracterizing the issue,” said Clarissa Martinez de Castro, with the National Council of La Raza, in a call for reporters.

Despite the disagreements, the tone of the hearing was serious and policy-minded. There were no calls to make life difficult for illegal immigrants to encourage them to “self-deport,” as advocated by 2012 Republican presidential nominee Mitt Romney, and only a couple references to “amnesty.”