President Obama on Tuesday unveiled his plan to secure a pathway to citizenship for 11 million illegal immigrants already living in the United States, trying to build momentum for long-stalled immigration reforms.

Looking to reverse what he described as the biggest failure of his first term, Obama's reform plan would impose the most sweeping changes to the national immigration system in decades. Obama's blueprint is similar to the bipartisan Senate plan released a day earlier, though there are important differences between them that ensure a showdown with Congress.

"We need Congress to act on a comprehensive approach that finally deals with the 11 million undocumented immigrants who are in this country right now," Obama told a largely Latino audience during a campaign-style visit to Las Vegas. "Do we have the resolve as a people, as a country, as a government to finally put this issue behind us? I believe that we do."

Differences between White House and Senate on immigration
» Senate plan wouldn't provide path to citizenship until U.S.-Mexico border was secured. President's plan doesn't link the two, allowing illegal immigrants to achieve citizenship sooner.
» President's plan gives same-sex couples the same status as heterosexual couples. The Senate plan doesn't address gay couples.

Like the Senate plan, Obama would require illegal immigrants to register with the government, pass background checks, pay fees and wait behind legal immigrants to get their green cards.

However, the president's plan differs from the Senate package in significant ways. The Senate plan wouldn't provide a pathway to citizenship until the U.S.-Mexico border was secured. Obama doesn't tie citizenship to border security, allowing illegal immigrants to achieve citizenship more quickly. The president's plan also grants gay couples the same status as heterosexual couples. The Senate plan doesn't address same-sex couples.

Hispanic activists immediately called on Obama to provide greater clarity on how he plans to achieve what could be the top legislative priority of his second term.

"It was yet another speech -- and there wasn't much new," said Alfonso Aguilar, executive director of the Latino Partnership for Conservative Principles. "There are two problems: There is no mention of a guest worker program. And Republicans and a lot of religious groups won't support visas for same-sex couples."

Obama, whose support for immigration reform earned him about 70 percent of the Hispanic vote in last November's election, is also facing major pressure from the political left, particularly from immigrant rights groups who note that his administration has deported more illegal immigrants than any other.

The president should "order suspending deportations as the first step to open a pathway to citizenship for undocumented immigrants," said Pablo Alvarado, executive director of the National Day Laborer Organizing Network. "Ceasing the deportation of those he states he wishes to legalize is what will give the president's speech meaning and what can distinguish it from similar speeches."

Though his blueprint largely mirrored the one offered by lawmakers, Obama vowed to forge ahead with his recommendations if talks break down on Capitol Hill, part of a newly aggressive tone for the second-term president.

"We can't allow immigration reform to get bogged down in an endless debate," he said. "And if Congress is unable to move forward in a timely fashion, I will send up a bill based on my proposal and insist that they vote on it right away."