“He is someone who has a tremendous amount of experience with legal policy issues that the committee has to involve itself in,” said Leonard Leo, the executive vice president of the Federalist Society, an organization of conservative lawyers.

His new role will also require Sessions to manage the minority staff, a task that University of Alabama law professor Bryan Fair said the senator is capable of doing, considering his past experience as a state attorney general.

“When he was attorney general he managed a large office with a number of divisions,” Fair said.

Senate Minority Whip Jon Kyl , an Arizona Republican and member of the Judiciary panel, cited Sessions’ background as a former U.S. attorney.

“He’s a real lawyer’s lawyer,” Kyl said. “He’s careful. You can tell a lawyer because he gets down into the weeds on things. Jeff does that because he really cares about things. I think he will be very sound.”

“Sen. Sessions is a scrapper,” said John Cornyn of Texas, a Judiciary Committee member and chairman of the National Republican Senatorial Committee, the Senate GOP’s political arm. “We’ve got an important job to do — investigate the background and qualifications of every nominee — and I hope we’ll have the time and be able to do that.”

Liberal groups, however, view Sessions with extreme wariness and are bracing for more partisan fights over judicial appointments. Senate Republicans have already challenged several of Obama’s picks on the grounds that their views on social issues are out of step.

Obama has reached out to Specter and Judiciary Committee member Orrin G. Hatch , R-Utah, about the Supreme Court vacancy, but he hadn’t called Sessions as of Monday evening.

“I think given his role on the committee, I suspect the hearings to be even more polarized and divisive in the future,” said Nan Aron, the president of the liberal group Alliance for Justice.

While the Clinton administration often worked with Specter on nominations, Sessions was part of a group of Republican senators who sought to hold up several nominees, including Marsha Berzon and Richard Paez to the U.S. Court of Appeals for the 9th Circuit.

“The ranking member has gone from being a person whom Democrats have worked well with to someone who has put holds on nominees,” said Benjamin Wittes, a Brookings Institution scholar and the author of “Confirmation Wars,” a book about judicial nominations.

Sessions has come down on both sides of the filibuster issue when it comes to confirming judges.

While Sessions was one of a number of Republicans demanding that President Bill Clinton’s judicial nominees clear the Senate’s 60-vote threshold, he was also one of the top critics of Democrats when they sought to filibuster President George W. Bush ’s nominees.

“It was not Republicans who started filibustering judges,” Sessions said in a 2005 floor exchange with California Democrat Sen. Barbara Boxer . “And it was an historic change in our procedures when the Democrats started doing it. It caused great pain and anguish.”

Restaffing Expected

Conservatives expect that Sessions will do some housecleaning on the Judiciary Committee’s minority staff. Specter had already agreed to hire conservative staff as part of a deal with fellow Republicans when he was named to chair the committee in 2005. But Jay Sekulow, the chief counsel of the American Center for Law and Justice, expects changes under Sessions.

“I assume he will bring in some conservative staff,” said Sekulow. He called Sessions’ elevation on the committee “good for Republicans.”

Sessions has tended to stick to the conservative line, particularly when it comes to the issues he cares most about: judicial nominations, immigration and crime. He has a 95 percent lifetime rating from the American Conservative Union.

But he’s shown a desire to work with Democrats to equalize federal sentences for offenses involving crack and powdered cocaine. Under current law, the possession of five grams of crack triggers a mandatory five-year prison sentence, while it takes 500 grams of powdered cocaine to bring on the same sentence. The lower sentencing threshold for crack has disproportionately affected African-Americans.

Although he is considered a loyal Republican, Sessions sharply criticized Bush’s push for comprehensive immigration policy overhaul in 2007. The legislation aimed to allow millions of illegal immigrants to earn citizenship while also boosting spending on border security and creating a temporary guest worker program.

His Own Confirmation Controversy

And Sessions brings a confirmation experience of his own to the job: President Ronald Reagan nominated him for a federal judgeship in 1986, when Sessions was a U.S. attorney for the Southern District of Alabama. But the Judiciary Committee took the rare step of killing the nomination. The committee first voted 8-10 against recommending that Sessions be confirmed. Then, on a 9-9 vote, the committee killed a motion to send the nomination to the Senate floor without any recommendation.

Opponents accused him of “gross insensitivity” on racial issues. Justice Department lawyers said he had called the NAACP and American Civil Liberties Union “communist-inspired,” and had said they tried to “force civil rights down the throats of people.” Sessions said his words were misrepresented.

Among the senators who voted against his nomination were Leahy, Specter and Joseph R. Biden Jr. , D-Del. (1973-2009), who is now the vice president.

Despite the sometimes acrimonious history with fellow senators, one of Sessions’ strong points is his ability to get along with his colleagues, said Wendy Long, a counsel for the Judicial Confirmation Network, which has been plotting strategy with other conservative groups on the coming Supreme Court hearings.

“Sessions is not an antagonistic person. He is personally very pleasant,” Long said. “He will be aggressive and thorough, but I don’t think he will allow the kind of game-playing and ‘gotcha’ that the Democrats have played.”

Judiciary Committee member Lindsey Graham , R-S.C., said Sessions would ensure that Republicans get enough time and assets to review nominees.

“Firm. Fair. Tenacious. He will hold their feet to the fire,” Graham said.

Unlike Specter, Sessions won’t have to convince anyone that he’s conservative enough, Graham said.

“Nobody is going to question his pedigree or his credentials,” Graham said. “It puts the burden on Jeff that he’s fair, and he will be. I have no doubt in my mind that he’ll be firm and fair.”

Kathleen Hunter, Seth Stern and Keith Perine contributed to this story.