The Senate on Thursday took up what a key senator called the "gigantic task" of tightening U.S. borders against illegal immigrants while also allowing those already here to stay as low-wage workers for American businesses.

The effort pits two Republican bases in an election-year fight against each other — social conservatives who want the government to take a harder line against illegal immigrants and employers who want those immigrants for jobs.

"I have seen virtually no agreement on anything. Emotions are at an all-time high," Senate Judiciary Committee Chairman Arlen Specter said, opening the first of several meetings by his panel for writing a bill.

Specter said he hoped his committee could have legislation ready by the end of March.

The House passed a border security bill last year — pleasing conservatives clamoring for an immigration crackdown. But that came only after House leaders beat back an attempt by some GOP members to include President Bush's proposal for a program giving illegal immigrants already here temporary worker status.

In contrast, the Senate is wading right into the thorny guest worker issue.

Specter said a solution is needed for the problem of 11 million illegal immigrants "in the shadows" of the country.

"Our first job is to bring them out of the shadows and that is a very big job," he said.

He acknowledged some Republicans want all illegal immigrants sent home, but said that if illegal immigrants know they will be kicked out when they "show up," then they will not come out of the shadows.

He also said he does not object to providing a tract to legalization for immigrants who work in the country as proposed by Sens. John McCain, R-Ariz., and Edward M. Kennedy, D-Mass. But, Specter added: "The political reality is that is going to be very difficult to do."

Bush called for a temporary worker proposal in January 2004, but it quickly got bogged down in election-year politics.

With the business lobby pressing on the issue, Bush has renewed his call for temporary visas for workers.

Pressure to move forward intensified this week as governors meeting in Washington said they consider immigration one of their major concerns and made it an agenda item in their private meetings with Bush and his Cabinet.

Specter's plan would allow immigrants who entered this country before Jan. 4, 2004, and who have jobs to participate for up to six years in the temporary worker program.

The bill and another proposed by Sens. John Cornyn, R-Texas, and Jon Kyl, R-Ariz., would force workers to return to their countries of origin if they want to become permanent legal U.S. residents.

The Cornyn-Kyl legislation goes further than Specter's and mandates that illegal immigrants leave the country within five years.

Sen. John McCain, R-Ariz., has been promoting his own immigration reform proposal in town halls around the country. His bill has the backing of the U.S. Chamber of Commerce, other business groups, immigration advocates and some labor unions.

His bill, co-authored by Sen. Edward Kennedy, D-Mass., would penalize employers who hire illegal workers but allows immigrants participating in the temporary worker program to work toward eligibility for legal permanent residence.

"I have serious concerns about Senator Specter's proposal and I hope that we can improve it," Kennedy said at a rally of immigration workers Wednesday.

Some Republicans, however, want to toughen up Specter's bill. Alabama Republican Sen. Jeff Sessions said Specter's proposal is "like someone trying to leap a 10-foot ravine and going 9 feet."

"It just doesn't get there on law enforcement," Sessions said.

He said the upcoming immigration debate will be a test for Congress on whether it wants immigration law enforced. He's expected to offer some amendments to Specter's bill, including one to allow local law officers to enforce immigration law.

Presidential politics is an undercurrent in the debate. Majority Leader Bill Frist, McCain and Nebraska Republican Sen. Chuck Hagel, who has pushed immigration legislation to provide a steady supply of workers for the agriculture industry, are considered potential 2008 presidential candidates.

Frist told several key senators early last month that he planned to take up immigration on the Senate floor March 27, leaving open the possibility that he might offer his own immigration bill if the Judiciary Committee did not yet have a consensus bill.