WASHINGTON (AFP) - A bipartisan group of top senators on Monday proposed a pathway to citizenship for many of the 11 million undocumented immigrants living in the United States (US), a plan hailed by the White House.

The proposal, unveiled by four Democrats and four Republicans after weeks of talks, appears to be the most serious attempt at immigration reform since 2007, when then president George W. Bush's effort failed to get through Congress.

President Barack Obama has made it clear that reforming what many have described as a "broken" immigration system is to be a top priority of his second term, which began on Jan 20.

The plan unveiled Monday by Republicans such as John McCain and Marco Rubio and Democrats Dick Durbin, Chuck Schumer and Robert Menendez would provide a "tough but fair" pathway to citizenship for most undocumented immigrants.

It would also include a strengthened employment verification system, beefed up border security such as drones and other surveillance, improved skill-based immigration, better visa enforcement, and deportation for serious criminals.

Mr Schumer said he was confident a deal could be struck within months.

"We still have a long way to go, but this bipartisan blueprint is a major breakthrough," Mr Schumer told a press conference.

"It is our hope that these principles can be turned into legislation by March... with the goal of passage out of the Senate by late spring or summer."

Other bipartisan groups of lawmakers have trumpeted similar proposals before, Mr Schumer said, "but we believe this will be the year Congress finally gets it done."

"For the first time ever, there is more political risk in opposing immigration reform than in supporting it," said the senator from New York.

Mr McCain said the politics of the issue have changed dramatically.

"If you look at the polls when it comes to immigration reform that includes a path to citizenship for certain immigrants without papers, the American people are there," he said.

But Mr McCain, from the border state of Arizona where illegal immigration remains a hot-button issue, said dramatic improvements along the border have also helped turn the tide.

At the White House, spokesman Jay Carney said Mr Obama "believes it is very important that we move forward on comprehensive immigration reform."

"It's the right thing to do for the country, for our economy. It's the right thing to do out of fairness to the middle class to make sure that everyone plays by the same set of rules," Mr Carney said.

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

Mr Obama will head to Nevada on Tuesday to "redouble the administration's efforts to work with Congress to fix the broken immigration system this year," the White House said.