Washington (CNN) -- A bipartisan group of U.S. senators at the heart of the debate over immigration reform toured the U.S.-Mexico border in Arizona on Wednesday -- the latest sign of growing legislative momentum on a polarizing issue that has been stalled on Capitol Hill for years.
Arizona GOP Sens. John McCain and Jeff Flake were joined on the tour by New York's Chuck Schumer and Colorado's Michael Bennet, both Democrats. The four men are part of a group of eight senators expected to unveil comprehensive legislation soon after Congress returns from its spring break in April.
President Barack Obama also stepped up his push for a comprehensive bill, sitting down for interviews with the Telemundo and Univision. While both interviews were embargoed, immigration was expected to dominate the discussion.
Speaking at a naturalization ceremony at the White House on Monday, Obama said he expects significant legislation action next month.
"We are making progress, but we've got to finish the job," the president said. "I want to sign that bill into law as soon as possible."
House Minority Leader Nancy Pelosi, D-California, told reporters Wednesday she is "optimistic" about the chances of legislative success.
Democrats and Republicans have been bogged down for years over the question of how best to secure the country's border while resolving the status of roughly 11 million undocumented immigrants. A rare political window appeared to open after last November's presidential election, when GOP presidential nominee Mitt Romney performed dismally among Hispanic voters.
Despite strong conservative resistance to a pathway to citizenship for undocumented immigrants, Republican leaders recognize their party's need to appeal more strongly to America's fastest growing minority group. For his part, Obama is hoping to lock in a major second term legislative victory.
A source familiar with the congressional negotiations has told CNN that the eight senators have tentatively reached agreement on some of the thorniest issues, such as a path to citizenship and metrics for securing the border.
The groups is also working on a revamped guest worker program, the source noted.
More specifically, one of the big outstanding issues appears to be around the future flow of low-skilled guest workers who would come to the United States to be maids, waiters, hotel workers or home-care workers. Negotiators are discussing how much they would be paid, and how many workers would be allowed into the country each year.
Labor unions influencing the talks are arguing for higher pay and fewer workers per year, since they are concerned about the effect guest workers would have on American workers. Groups such as the Chamber of Commerce, however, are pushing senators for lower pay and high numbers of guest workers per year, since that will help businesses' bottom lines.
On the issue of permanent legal status, the source told CNN the senators have essentially agreed to a 13 year path to citizenship. According to the tentative agreement, it would take 10 years for illegal workers to get a green card to work legally in the U.S. and then an additional three years to move towards citizenship.
Illegal workers would have to pay a fine, back taxes, and have no criminal record.
The senators, according to the source, have agreed that no illegal worker will be eligible for citizenship until the border is considered secure. Figuring out how to measure that has been a major part of the talks.
Others senators involved in the immigration talks include: Sen. Lindsey Graham, R-South Carolina; Sen. Marco Rubio, R-Florida; Sen. Robert Menendez, D-New Jersey; and Sen. Dick Durbin, D-Illinois.
Senate Judiciary Committee Chairman Patrick Leahy, D-Vermont, sent a letter to several strong Senate conservatives last week urging them not to obstruct the upcoming legislative process relating to the issue.
"I hope it is not your intention to discredit the process," Leahy said. "I intend to proceed to comprehensive immigration reform with all deliberate speed. ... I hope and expect that you will not delay consideration simply to prevent the legislation from moving forward."
"Artificial delays, delays for delays' sake, has tainted too much of the Senate's work over the last few years," he added.
Leahy's letter was sent to Alabama GOP Sen. Jeff Sessions, a high ranking member of the committee. Committee Republicans Chuck Grassley of Iowa, Orrin Hatch of Utah, Mike Lee of Utah, John Cornyn of Texas, and Ted Cruz of Texas also received copies of the letter.
CNN's Dana Bash, Alex Mooney, Laurie Ure contributed to this report.