* Expected to be Senate's final vote of year
* Anticipated confirmation set for Jan. 6
* Senate expected to confirm on Friday new IRS chief
By Thomas Ferraro
WASHINGTON, Dec 20 (Reuters) - The Democratic-led U.S. Senate is expected to wrap up its work for the year on Friday by moving to clear President Barack Obama's nomination of Janet Yellen to head the Federal Reserve.
But under a bipartisan agreement reached on Thursday, the Senate will not vote to confirm Yellen, now the Fed's vice chair, until Jan. 6, the day it returns for the new year. She would replace Ben Bernanke, whose term ends in late January.
The Senate is to vote at about mid-day on Friday on whether to bring debate on Yellen to a close. To prevail on this test vote and advance the nomination, Obama's Democrats, who hold the Senate, 55-45, need a simple majority and seem certain to get it.
Friday's vote on Yellen is expected to be the final Senate vote of the year.
Under the bipartisan agreement, the Senate on Friday is also expected to confirm three other Obama nominees: Alejandro Mayorkas as deputy secretary of the Department of Homeland Security; John Koskinen to head the Internal Revenue Service, and Brian Davis to be a federal judge in Florida.
Republicans refused requests by Democrats to carry over until next year six other Obama nominees, all to relatively low-level posts.
That means they face the prospect of having to start the confirmation process all over again with Obama renominating them.
The stage was set for this end-of-year confirmation battle when Democrats changed the Senate rules last month to strip Republicans of their power to block most of Obama's nominees with procedural roadblocks known as filibusters.
Republicans accused Democrats of an unwarranted power grab. Democrats said they did it to combat unprecedented Republican obstructionism.
Under the new rules, a nominee needs the support of only a simple majority of the 100-member Senate, rather than the earlier 60, to be confirmed.
The change, however, did not strip Republicans of their ability to slow down matters by refusing to yield back allotted debate time, which for a Cabinet-level nominee such as Yellen is 30 hours. For most lower-level picks, Democrats and Republicans get four hours each.
Earlier Thursday, before reaching an agreement with Republicans to end gridlock on the nominees, Reid vowed to get all the picks confirmed and aimed to get Yellen approved on Saturday.
"These are crucial nominations, and if that means working through the weekend and next week, so be it," Reid said.
Assistant Senate Republican Leader John Cornyn said, "The irony is that none of these nominations are particularly urgent."
"Even Ms. Yellen - Bernanke's term doesn't end until the end of January - so this is all gratuitous from my perspective," Cornyn said.
McConnell said he would oppose the IRS nominee, denouncing as inadequate a probe into the tax-collection agency's "abuse of power" in targeting conservative groups for added scrutiny.
"The American people deserve answers about how and why this targeting happened," McConnell said. "And I will not be supporting any nominee to lead this agency until the American people get the answers they deserve."
Reid urged confirmation of Koskinen to head the IRS, saying, "With all the problems we've had with the Internal Revenue Service ... we need to have someone running that agency."