WASHINGTON: Eight US lawmakers crossed party lines to unveil a plan Monday that would provide a pathway to citizenship for 11 million illegal immigrants currently living in the shadows in the United States.

"We recognize that our immigration system is broken," the senators said in their bipartisan framework, which comes as President Barack Obama vows a fresh push on immigration in his second term.

It promises a "tough but fair" path to citizenship for undocumented immigrants, reform that would build the US economy, an "effective" employment verification system and an improved process to admit future workers.

The proposed legislation also increases the number of drones and other surveillance equipment, as well as the number of agents at and between ports of entry in a bid to better secure the long borders the United States shares with Canada to the north and especially Mexico to the south.

Senators backing the measure are Republicans John McCain, Marco Rubio, Lindsey Graham and Jeff Flake, along with Democrats Robert Menendez, Chuck Schumer, Dick Durbin and Michael Bennet.

Rubio's Republican support would be vital to any deal going forward. He has spoken in recent weeks about his immigration stance, which includes a multi-step pathway to citizenship, as well as improved skill-based immigration, visa enforcement and border safety and enforcement.

"We can't round up millions of people and deport them," Rubio, the son of Cuban immigrants, wrote in an opinion article published in the Las Vegas Review-Journal ahead of Obama's visit to the state of Nevada on Tuesday.

"But we also can't fix our broken immigration system if we provide incentives for people to come here illegally -- precisely the signal a blanket amnesty would send."

Although the bill seeks to boost security measures, it also vows to "strengthen prohibitions against racial profiling and inappropriate use of force," as well as improve training for border patrol agents and increase oversight.

In a bid to combat visa overstays, the lawmakers offered a requirement for those in the country illegally to register with the government.

Around 40 percent of the illegal immigrants now in the United States entered the country legally but then let their visa expire, according to official estimates.

But under the plan, they would also be able to earn "probationary" legal status -- to live and work legally in the US -- after passing a background check and paying a fine and back taxes.

Those with a "serious" criminal background or who otherwise threaten US national security would not be eligible for legal status and would face deportation, according to the framework document.

"Individuals with probationary legal status will be required to go to the back of the line of prospective immigrants" and pass an additional background check, among other requirements, the document said.

Under the plan, individuals who fulfill the requirements could eventually obtain a green card for permanent residency.

On Sunday, the bitterly divided lawmakers expressed optimism they could unite on immigration reform.

"I'm confident, guardedly optimistic, that this time we can get it done," McCain told ABC television's "This Week," confirming that Republican and Democratic senators had been meeting on the issue in recent weeks.

McCain, who once championed comprehensive reform but backtracked during his failed 2008 presidential run, said there was a greater willingness to address the issue after last year's election, in which the increasingly important Hispanic vote swung strongly behind Obama's Democrats.

He also acknowledged that Republicans were "losing dramatically" the Hispanic vote.

Menendez, a New Jersey Democrat who attended a meeting on Friday between Obama and congressional Hispanic leaders, said he too was "cautiously optimistic."

"I see the right spirit. I see things that were once off the table for agreement and discussion being on the table with a serious pathway forward," he said.

During Obama's Nevada trip, his first since being sworn in last week for a second term, Obama will "redouble the efforts to work with Congress to fix the broken immigration system this year," the White House said.

A bill backed by Obama that would have legalized the status of many of the undocumented immigrants living in the United States died in Congress at the end of 2010 because of opposition from Republicans, including Rubio.

Reforming America's aging immigration system is the only major issue that has generated some degree of political consensus since the November elections.

Hispanics voted massively for Obama, flexing their growing political heft in several key states, and since then Republican leaders and well-known conservative commentators have jumped on the reform bandwagon.