WASHINGTON - A bipartisan group of leading senators has reached agreement on the principles of sweeping legislation to rewrite the nation's immigration laws.

The deal, which was to be announced at a news conference Monday afternoon, covers border security, guest workers and employer verification, as well as a path to citizenship for the 11 million illegal immigrants already in the United States.

Although thorny details remain to be negotiated and success is far from certain, the development heralds the start of what could be the most significant effort in years toward overhauling the nation's inefficient patchwork of immigration laws.

President Obama also is committed to enacting comprehensive immigration legislation and will travel to Nevada on Tuesday to lay out his vision, which is expected to overlap in important ways with the Senate effort.

The eight senators expected to endorse the new principles Monday are Democrats Charles Schumer of New York, Dick Durbin of Illinois, Robert Menendez of New Jersey and Michael Bennet of Colorado; and Republicans John McCain of Arizona, Lindsey Graham of South Carolina, Marco Rubio of Florida and Jeff Flake of Arizona.

In a statement, White House Deputy Press Secretary Josh Earnest said, "As the President has made clear for some time, immigration reform is an important priority and he is pleased that progress is being made with bipartisan support. At the same time, he will not be satisfied until there is meaningful reform and he will continue to urge Congress to act until that is achieved. The President looks forward to redoubling the administration's efforts to work with Congress on this important issue this week."

Several of these lawmakers have worked for years on the issue. McCain collaborated with the late Democratic Sen. Edward M. Kennedy on comprehensive immigration legislation pushed by then-President George W. Bush in 2007, only to see it collapse in the Senate when it couldn't get enough GOP support.

Now, with some Republicans chastened by the November elections which demonstrated the importance of Latino voters and their increasing commitment to Democrats, some in the GOP say this time will be different.

"What's changed, honestly, is that there is a new, I think, appreciation on both sides of the aisle -- including maybe more importantly on the Republican side of the aisle -- that we have to enact a comprehensive immigration reform bill," McCain said Sunday on ABC's "This Week."

"I think the time is right," McCain said.

The group claims a notable newcomer in Rubio, a potential 2016 presidential candidate whose conservative bona fides may help smooth the way for support among conservatives wary of anything that smacks of amnesty.

In an opinion piece published Sunday in the Las Vegas Review-Journal, Rubio wrote that the existing system amounts to "de facto amnesty," and he called for "commonsense reform."

The group says in a statement, "We recognize that our immigration system is broken. And while border security has improved significantly over the last two Administrations, we still don't have a functioning immigration system. This has created a situation where up to 11 million undocumented immigrants are living in the shadows. Our legislation acknowledges these realities by finally committing the resources needed to secure the border, modernize and streamline our current legal immigration system, while creating a tough but fair legalization program for individuals who are currently here. We will ensure that this is a successful permanent reform to our immigration system that will not need to be revisited."