* Immigrant farmworker details still in play
* Senate could debate bill in May
By Charles Abbott and Richard Cowan
WASHINGTON, April 9 (Reuters) - Senate negotiators on Tuesday were putting the finishing touches on a bipartisan immigration bill as labor and agriculture groups argued about restrictions on immigrant farmworkers and their pay, lawmakers and officials involved in the negotiations said.
"We're making progress. We're trying to get it done this week," Senator John McCain told reporters.
The Arizona Republican is one of eight Democrats and Republicans in the Senate trying to cobble together a complicated bill that would update U.S. immigration laws for the first time since 1986.
In recent weeks, labor unions and the U.S. Chamber of Commerce reached tentative agreement on the handling of low-skilled workers from foreign countries who would work as construction laborers, maids and waiters.
That left one big unresolved matter: the rules for bringing foreign farmworkers into the United States to harvest crops, milk cows and work on poultry and cattle operations.
U.S. Agriculture Secretary Tom Vilsack recently estimated that of the 1.1 million workers in agriculture, 500,000-700,000 are undocumented.
At a speech this week to agriculture journalists, Vilsack said that assuring a strong labor supply is a matter of importing workers versus importing food. "We risk the possibility of some of the work we do in this country moving to other nations," he said.
The agriculture industry and farmworker groups have been haggling over the cap that would be set under the Senate bill for foreign farm labor, whether those already in the United States would be allowed to stay and pay levels for the temporary workers.
"We want to make sure farmworkers are making at least as much money as they are today, not less," Diana Tellefson Torres, a United Farm Workers vice president, told the North American Agricultural Journalists meeting.
Craig Regelbrugge, co-chair of an agriculture industry coalition, said labor can account for one-third of the cost of production of fruits and vegetables, so wage rates are important. Noting the need for a high cap on farmworker visas compared to other sectors, he said, "what's different about agriculture is it's the nation's food supply."
But some labor groups fear that too many foreign workers would depress U.S. wages or kill some American jobs.
Regelbrugge said there are discussions of a new visa that would run more than 12 months so immigrant laborers do not have to routinely exit the U.S. for brief periods, leaving farms short-handed. While some growers need help only at harvest, dairies and livestock feeders need workers all year.
FAST-TRACK IN SENATE
The linchpin of the immigration bill would end deportation fears for most of the approximately 11 million people who are living in the United States illegally, many from Central America and Asia. The legislation would eventually put many of them on a path to citizenship, if further progress was made in securing the southwestern border with Mexico.
The eight senators outlined their proposal in late January and have been struggling to fill in the details of a bill that could move quickly through the Senate once it is unveiled.
If a bill is introduced by Monday, Senate aides said it could be debated, and possibly amended, in the Senate Judiciary Committee by April 18, with a committee vote by April 25, just before the start of a week-long Senate recess.
Under this accelerated timetable, Senate Majority Leader Harry Reid would try to schedule a full Senate debate in May.
However, delays are possible at any point in the process.
Republicans, who have opposed any moves to grant citizenship to undocumented residents, began taking an active interest in immigration changes after Hispanic-Americans voted against them in droves in the November 2012 election.
With the 2014 congressional elections around the corner, immigration reform advocates are hoping Congress can handle this issue in 2013, before campaign rhetoric heats up and possibly spoils chances for a bipartisan deal.
Supporters also want a strong, bipartisan showing in the Senate for legislation, which they think will propel it through the Republican-controlled House of Representatives, where there are more conservatives lawmakers who could reject a pathway to citizenship for the undocumented.
The House might try to pass immigration bills in a piecemeal fashion that could be merged with a Senate-passed bill. Some aides have said the House bill might require a longer wait time than the Senate bill for undocumented residents to earn citizenship - as long as 15 years, versus 10 to 13 years in the Senate bill. (Additional reporting by Rachelle Younglai; Editing by Stacey Joyce)