A bipartisan group of senators has agreed on a set of principles for a sweeping overhaul of the immigration system, including a pathway to U.S. citizenship for 11 million illegal immigrants that would hinge on progress in securing the borders and ensuring that foreigners leave the country when their visas expire.

The senators were able to reach a deal by incorporating the Democrats' insistence on a single comprehensive bill that would not deny eventual citizenship to illegal immigrants, with Republican demands that strong border and interior enforcement had to be clearly in place before Congress could consider legal status for illegal immigrants.

Their blueprint, set to be unveiled today, will allow them to stake out their position one day before President Barack Obama outlines his immigration proposals in a speech Tuesday in Las Vegas, in the opening moves of what lawmakers expect will be a protracted and contentious debate on the issue in Congress this year.

Lawmakers said they were optimistic that the political mood had changed since a similar effort collapsed in acrimony in 2010. Sen. John McCain, R-Ariz., and one of the negotiators, said he saw "a new appreciation" among Republicans of the need for an overhaul.

"Look at the last election," McCain said Sunday morning on ABC's "This Week With George Stephanopoulos." "We are losing dramatically the Hispanic vote, which we think should be ours." The senator also said he had seen "significant improvements" in border enforcement, although he said that "we've still got a ways to go."

According to a five-page draft of the plan obtained by The New York Times on Sunday, the eight senators have agreed to address the failings of the immigration system in one comprehensive measure, rather than in smaller pieces. Compared with an immigration blueprint from 2011 that White House officials have said is the basis for the president's position, the senators' proposals appear to include tougher enforcement and a less direct path for illegal immigrants than Obama is considering.

In a parallel effort, a separate group of four senators will introduce a bill this week dealing with another thorny issue: visas for legal immigrants with advanced skills in technology and science. The bill would nearly double the number of temporary visas, known as an H-1B, available each year to highly skilled immigrants. It would also free up more permanent resident visas, known as green cards, so those immigrants could eventually settle in the United States and go on to become citizens.