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The U.S. Senate is expected to cast a crucial vote Saturday on the DREAM Act, which would pave the way for possibly hundreds of thousands of undocumented immigrants to legalize their status.

And both opponents and supporters of the DREAM Act cranked up their arguments Friday, with Republican congressional leaders sending out a long list of reasons why the measure would be harmful for the country, and Democrats countering that not passing it would be detrimental.

Even Department of Homeland Security officials, including the heads of the main immigration agencies, joined the down-to-the-wire blitz, urging the passage of the DREAM Act.

Thursday night, Senate Majority Leader Harry Reid, D-Nev., scheduled the vote on the highly controversial measure, which would make undocumented immigrants younger than 30 years of age eligible for conditional legal status if they meet a strict set of criteria.

The so-called cloture vote would not be on the bill itself, but on whether to move toward a debate and then vote on the bill. Also on the schedule for a cloture vote is the bill that would repeal the ban on gays serving openly in the military.

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“I filed cloture on two important bills tonight,” said Reid Thursday evening. “We will soon vote on a bill that provides young people brought here by their parents with a path to citizenship through academic achievement or military service."

The DREAM Act, which passed in the House of Representatives by a vote of 216-198 on Dec. 8, is considered likely to have a tough time in the Senate.

Democrats need 60 votes to win cloture, and that means persuading some 10 Republicans to support it – a difficult feat, even the most hopeful proponents of the act have admitted.

“If they don’t reach the 60 votes for cloture, effectively that would be the end of the line for the DREAM Act,” said Grisella Martínez, director of policy and legislative affairs for the National Immigration Forum, which favors the DREAM Act.

One of the Republicans, Scott Brown of Massachusetts, whom DREAM Act supporters had hoped to persuade to vote for the measure, told reporters this week that he considered the bill “back-door amnesty.”

Opponents see DREAM, which stands for Development, Relief and Education for Alien Minors, as a reward for people who broke immigration laws. Republicans in Congress have assailed Reid and other Democrats for attempting to push through controversial measures during the lame-duck session.

Jeff Sessions, the top Republican on the Senate Judiciary Committee, which oversees immigration policy, urged his colleagues to oppose cloture.

Republicans on the committee sent out an e-mail today saying that the DREAM Act would lead to “increased unemployment of U.S. citizens, public education costs, chain migration, litigation and fraud.”

“Passing amnesty will incentivize even more illegality,” the e-mail said, “and lawlessness at the border. . .a large portion of those who receive amnesty will obtain jobs, but there is no surplus of job opportunities.”

Democrats have conceded that they wanted to make one more aggressive push for the bill now, before Republicans take control of the House next year. They say there is little likelihood that any measures allowing undocumented immigrants to legalize their status will pass in the new Congress.

Supporters say that children should not be punished for the decisions of their parents.

The measure would give conditional legal status to undocumented immigrants who came to the United States before the age of 16, are of good moral character, have a U.S. high school diploma or the equivalent, and attend college or serve in the military for at least two years. If they meet all the criteria, they eventually can apply for legal permanent residency, or the "green card."

The DREAM Act, in various variations, has tended to be part of broader immigration reform bills that have failed to pass in Congress over the years.

In 2007, a Senate cloture vote on the DREAM Act as a standalone bill failed.

Groups that favor strict immigration enforcement have been lobbying Senate members not to support what they call amnesty, and the erosion of respect for the nation's laws. Others, including undocumented students, spent Friday visiting congressional offices, making a last pitch for their case.

Department of Homeland Security officials also made an appeal in favor of the DREAM Act. They included all the heads of the various immigration agencies, including U.S. Immigration and Customs Enforcement, or ICE, which is charged with detaining and deporting illegal immigrants.

The DREAM Act, their press release said,  will have an "important role. . .in promoting public safety through smart and effective immigration enforcement."

"The DREAM Act," they said, "establishes a lengthy and rigorous process for young people who grew up in the United States to obtain legal status by either pursuing a higher education or by serving in the U.S. armed forces."

Today Rep. Luís Gutiérrez, an Illinois Democrat who led the fight for the DREAM Act in the House, issued a statement that said: “I want Republicans in the Senate -- and Democrats -- to stand with a generation of young immigrants and the children of immigrants who are struggling to find their place in American history.”

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