(Corrects to show Marco Rubio is a possible White House contender in 2016)
* Reform would establish new guest worker program
* Eight senators putting comprehensive agreement into bill
* Deal reached between labor federation and business
By Thomas Ferraro and Steve Holland
WASHINGTON, March 31 (Reuters) - With U.S. business and labor now in agreement, a bipartisan group of U.S. senators has resolved all major issues in a pending deal to overhaul the U.S. immigration system and aims to unveil it after Congress reconvenes in the second week of April, key lawmakers said on Sunday.
The lawmakers said that while there was no final deal yet, they hope and even expect there to be one soon after the measure is put into legislative language so all eight senators in the bipartisan group can review it.
The U.S. Chamber of Commerce, the biggest U.S. business group, and the AFL-CIO, the largest labor federation, reached an elusive agreement on a guest worker program on Friday, clearing the way for the writing of a full bill.
The bill will include an earned pathway to U.S. citizenship for an estimated 11 million undocumented immigrants, bolstered border security and ways for business to meet the need for both high-skilled and low-skilled workers.
"With the agreement between business and labor, every major policy issue has been resolved," said Senator Charles Schumer, a New York Democrat and a leader of the so-called Gang of Eight, which has four Democrats and four Republicans.
"We've all agreed that we're not going to come to a final agreement until we see draft legislative language and we agree on that," Schumer told NBC's "Meet the Press."
But Schumer added, "I don't think any of us expect there to be problems."
Republican Senator Jeff Flake of Arizona, another member of the group, also appeared on "Meet the Press," and said: "We're committed to this if we can get the language right."
Republican Senator Lindsey Graham of South Carolina, another member of the group, said: "I think we've got a deal."
"There are a few details yet," he said on CNN's "State of the Union" program. "But conceptually we have an agreement between business and labor, between ourselves that has to be drafted. It will be rolled out next week."
Graham voiced confidence that the bill would eventually be approved by the Democratic-led Senate and Republican-led House of Representatives - provided President Barack Obama, as expected, actively rallies support for it.
The Gang of Eight had initially planned to have a bill by the end of March, but now plans to unveil it in the week of April 8, when Congress returns from a two-week recess.
Republican Senator Marco Rubio of Florida, another member of the Gang of Eight and a potential 2016 White House contender, said the senators had made "substantial progress" on a deal, but were not yet finished.
"I'm encouraged by reports of an agreement between business groups and unions on the issue of guest workers. However, reports that the bipartisan group of eight senators have agreed on a legislative proposal are premature," Rubio said in a statement issued by his office.
Still, Rubio said, "I believe we will be able to agree on a legislative proposal that modernizes our legal immigration system, improves border security and enforcement and allows those here illegally to earn the chance to one day apply for permanent residency contingent upon certain triggers being met."
Rubio, the son of Cuban immigrants, made it clear that all should expect a lengthy legislative process.
"We will need a healthy public debate that includes committee hearings and the opportunity for other senators to improve our legislation with their own amendments," he said.
Schumer served as a mediator in a conference call on Friday between the head of the U.S. Chamber of Commerce, Tom Donohue, and the president of the AFL-CIO, Richard Trumka, a source said.
A guest-worker program has been a major stumbling block to the Gang of Eight, which has been working to try to reach a deal since December. The thorny issue has derailed other immigration-reform efforts over the years.
Labor unions have argued against such a program, worrying that a flood of low-wage immigrant laborers will take away jobs from Americans. The agreement covers pay levels for low-skilled workers and provides labor protections for American workers.
A new "W Visa" would be created for employers to petition for foreign workers in lesser skilled, non-seasonal non-agricultural occupations. This could include jobs in hospitality, janitorial, retail, construction and others.
The W Visa would not be considered a temporary visa, as workers would have the ability to seek permanent status after a year, according to details of the agreement released by the AFL-CIO.
The program would begin on April 1, 2015, unless there is a need to extend the start date by six months.
At the beginning, 20,000 visas would be permitted and the figure would rise to 35,000 the next year, 55,000 in the third year and 75,000 in the fourth. Under the agreement, the number of visas permitted in any year can never be less than 20,000 or more than 200,000.
The Gang of Eight began forming a day after the November 2012 elections, which saw Hispanics, the fastest growing voter bloc, heavily favor Democrats over Republicans.
The election experience has made Republicans realize that for their own political good they need to get behind immigration reform, something that has been primarily embraced by Democrats. (Reporting by Thomas Ferraro; Additional reporting by David Brunnstrom; Editing by David Brunnstrom)