LAS VEGAS -- Seizing an opening to rewrite the nation's immigration laws, President Barack Obama challenged Congress on Tuesday to act swiftly to put 11 million illegal immigrants living in the United States on a clear path to citizenship.
But his push for speedy action and his silence on proposals to defer the opportunity for legal residency until the nation's borders are deemed secure provoked criticism from a Republican leader on the issue. The response suggests that reaching consensus on immigration law changes remained difficult despite a new bipartisan push since the November elections.
Speaking at a high school in a state that has seen rapid growth in its Hispanic population, the president praised a bipartisan group of senators who proposed their own sweeping immigration overhaul a day earlier, saying their plan was very much in line with his own proposals.
Mr. Obama warned, however, that "the closer we get, the more emotional this debate is going to become." He said that if Congress did not move forward "in a timely fashion" on its own legislation, he would send up a specific measure -- action the White House has put off for now -- and demand a vote.
The president's speech immediately exposed potential fault lines in the coming debate. He said, for example, that there must be a path to citizenship for illegal immigrants "from the outset," a statement that would seem at odds with the assertion by some senators that citizenship must be tied to tighter border security.
Sen. Marco Rubio, R-Fla., who is seen as an influential party voice on an issue that cost Republicans in last year's voting, said he was "concerned by the president's unwillingness to accept significant enforcement triggers before current undocumented immigrants can apply for a green card." He continued: "Without such triggers in place, enforcement systems will never be implemented, and we will be back in just a few years dealing with millions of new undocumented people in our country."
Although Mr. Obama did not say it in his speech, the White House is also proposing that the United States treat same-sex couples the same as other families, meaning that people would be able to use their relationship as a basis to obtain a visa -- another element likely to be resisted by some conservative Republicans.
Brendan Buck, spokesman for House Speaker John Boehner, R-Ohio, said in a statement that House Republicans "hope the president is careful not to drag the debate to the left and ultimately disrupt the difficult work that is ahead in the House and Senate."
Mr. Obama offered a familiar list of proposals: tightening security on borders, cracking down on employers who hire illegal immigrants and temporarily issuing more visas to clear the huge backlog of people applying for legal status in the country.
The president's speech, on the heels of Monday's bipartisan Senate proposal, sets the terms for one of the year's landmark legislative debates. These are only the opening steps in a complicated dance, and both the politics and policy can be treacherous ground, as shown by the failed immigration overhaul bid in the George W. Bush administration.
But the flurry of activity underscores the powerful new momentum behind an overhaul of the system, after a presidential election that dramatized GOP vulnerability on the issue, with Mr. Obama piling up lopsided majorities over Republican Mitt Romney among Hispanic voters.
"Most Americans agree that it's time to fix a system that's been broken for too long," Mr. Obama said to about 2,000 high school students, many of them Hispanic. They applauded loudly when he mentioned the Dream Act, which offers amnesty to children of immigrants who are in the United States illegally.
In scrambling to present their blueprint Monday, the day before Mr. Obama's speech, the senators stole a march on the president. But their intent appeared less to undermine his efforts than to stake out their own role in drafting a comprehensive bill.
With the senators hoping to pass legislation by this summer, the White House has shelved, for now, plans to introduce its own immigration bill, officials said. Indeed, after two years of feuding with Congress, Mr. Obama finds himself in rare alignment with Democratic and Republican lawmakers on at least the need to address a major issue.
That is what made Mr. Obama's speech such a novelty: rather than criticize Congress as do-nothing and obstructionist, as he did nearly every day during the campaign, he applauded the lawmakers for racing ahead of him, at least for a day.
Among the main differences to be worked out is whether to make the path to citizenship for illegal immigrants contingent on stricter border controls and visa procedures. In his remarks, Mr. Obama emphasized that as long as immigrants registered with authorities and fulfilled other obligations such as paying their taxes, there should be no doubt that they would eventually obtain citizenship. "If you're able to meet some basic criteria," he said, "we'll offer you the chance to come out of the shadows."
The president's goal, the officials said, will be less to underline differences with the bipartisan plan than to marshal public support for comprehensive immigration legislation. Mr. Obama, having failed to achieve that in his first term, has put it at the top of his agenda for his second.